Rainer Helmig

(Journal-) Articles

1. Vahabzadeh, E., Buntic, I., Nazari, F., Flemisch, B., Helmig, R., & Niasar, V. (2025). Applicability of the Vertical Equilibrium model to underground hydrogen injection and withdrawal. International Journal of Hydrogen Energy, 106, 790–805. https://doi.org/10.1016/j.ijhydene.2025.01.201
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   Abstract

   Underground hydrogen storage (UHS) has emerged as a significant focus for the energy transition from fossil fuels to renewable energy. Saline aquifers, akin to those used in geological CO2 storage, are proposed due to their potential as reservoirs for hydrogen injection and withdrawal over extended periods. Modeling the drainage and imbibition processes at the reservoir scale is critical for efficient UHS implementation. To address the excessive computational costs of three-dimensional simulations over hundreds of cycles, low-order models such as the Vertical Equilibrium (VE) models offer practicality. This study centers on the VE model’s applicability to predict hydrogen plume shapes during a single injection and withdrawal cycle, considering varying viscous, capillary, and buoyancy forces, captured by Capillary number (Ca) and Bond number (Bo). Examining Ca values from 1.5 × 10−9 to 1.5 × 10−7 and Bo numbers from 0.1 to 0.3, we compared VE results to a 2D two-phase simulation, serving as the reference solution. For small Ca, the VE method accurately predicted both vertical and horizontal hydrogen plume distributions, although it occasionally overestimated lateral spread at high injection rates. As the vertical permeability and Bo increase, the VE predictions become more aligned with the reference solution. This is because greater density-driven flow and improved vertical connectivity make the phase segregation easier. Our study also demonstrated the VE model’s promising performance in hydrogen recovery during withdrawal at small Ca and large Bo.

   BibTeX

   @article{applicabilityOfVE2025, abstract = {Underground hydrogen storage (UHS) has emerged as a significant focus for the energy transition from fossil fuels to renewable energy. Saline aquifers, akin to those used in geological CO2 storage, are proposed due to their potential as reservoirs for hydrogen injection and withdrawal over extended periods. Modeling the drainage and imbibition processes at the reservoir scale is critical for efficient UHS implementation. To address the excessive computational costs of three-dimensional simulations over hundreds of cycles, low-order models such as the Vertical Equilibrium (VE) models offer practicality. This study centers on the VE model’s applicability to predict hydrogen plume shapes during a single injection and withdrawal cycle, considering varying viscous, capillary, and buoyancy forces, captured by Capillary number (Ca) and Bond number (Bo). Examining Ca values from 1.5 × 10−9 to 1.5 × 10−7 and Bo numbers from 0.1 to 0.3, we compared VE results to a 2D two-phase simulation, serving as the reference solution. For small Ca, the VE method accurately predicted both vertical and horizontal hydrogen plume distributions, although it occasionally overestimated lateral spread at high injection rates. As the vertical permeability and Bo increase, the VE predictions become more aligned with the reference solution. This is because greater density-driven flow and improved vertical connectivity make the phase segregation easier. Our study also demonstrated the VE model’s promising performance in hydrogen recovery during withdrawal at small Ca and large Bo.}, author = {Vahabzadeh, Ehsan and Buntic, Ivan and Nazari, Farzaneh and Flemisch, Bernd and Helmig, Rainer and Niasar, Vahid}, doi = {https://doi.org/10.1016/j.ijhydene.2025.01.201}, issn = {0360-3199}, journal = {International Journal of Hydrogen Energy}, pages = {790-805}, title = {Applicability of the Vertical Equilibrium model to underground hydrogen injection and withdrawal}, url = {https://www.sciencedirect.com/science/article/pii/S036031992500223X}, volume = 106, year = 2025 }

   Link

   https://www.sciencedirect.com/science/article/pii/S036031992500223X
2. Aricò, C., Helmig, R., Puleo, D., & Schneider, M. (2024). A new numerical mesoscopic scale one-domain approach solver for free fluid/porous medium interaction. Computer Methods in Applied Mechanics and Engineering, 419, 116655. https://doi.org/10.1016/j.cma.2023.116655
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   Abstract

   A new numerical continuum one-domain approach (ODA) solver is presented for the simulation of the transfer processes between a free fluid and a porous medium. The solver is developed in the mesoscopic scale framework, where a continuous variation of the physical parameters of the porous medium (e.g., porosity and permeability) is assumed. The Navier–Stokes–Brinkman equations are solved along with the continuity equation, under the hypothesis of incompressible fluid. The porous medium is assumed to be fully saturated and can potentially be anisotropic. The domain is discretized with unstructured meshes allowing local refinements. A fractional time step procedure is applied, where one predictor and two corrector steps are solved within each time iteration. The predictor step is solved in the framework of a marching in space and time procedure, with some important numerical advantages. The two corrector steps require the solution of large linear systems, whose matrices are sparse, symmetric and positive definite, with M-matrix property over Delaunay-meshes. A fast and efficient solution is obtained using a preconditioned conjugate gradient method. The discretization adopted for the two corrector steps can be regarded as a Two-Point-Flux-Approximation (TPFA) scheme, which, unlike the standard TPFA schemes, does not require the grid mesh to be K-orthogonal, (with K the anisotropy tensor). As demonstrated with the provided test cases, the proposed scheme correctly retains the anisotropy effects within the porous medium. Furthermore, it overcomes the restrictions of existing mesoscopic scale one-domain approaches proposed in the literature.

   BibTeX

   @article{ARICO2024116655, abstract = {A new numerical continuum one-domain approach (ODA) solver is presented for the simulation of the transfer processes between a free fluid and a porous medium. The solver is developed in the mesoscopic scale framework, where a continuous variation of the physical parameters of the porous medium (e.g., porosity and permeability) is assumed. The Navier–Stokes–Brinkman equations are solved along with the continuity equation, under the hypothesis of incompressible fluid. The porous medium is assumed to be fully saturated and can potentially be anisotropic. The domain is discretized with unstructured meshes allowing local refinements. A fractional time step procedure is applied, where one predictor and two corrector steps are solved within each time iteration. The predictor step is solved in the framework of a marching in space and time procedure, with some important numerical advantages. The two corrector steps require the solution of large linear systems, whose matrices are sparse, symmetric and positive definite, with M-matrix property over Delaunay-meshes. A fast and efficient solution is obtained using a preconditioned conjugate gradient method. The discretization adopted for the two corrector steps can be regarded as a Two-Point-Flux-Approximation (TPFA) scheme, which, unlike the standard TPFA schemes, does not require the grid mesh to be K-orthogonal, (with K the anisotropy tensor). As demonstrated with the provided test cases, the proposed scheme correctly retains the anisotropy effects within the porous medium. Furthermore, it overcomes the restrictions of existing mesoscopic scale one-domain approaches proposed in the literature.}, author = {Aricò, Costanza and Helmig, Rainer and Puleo, Daniele and Schneider, Martin}, doi = {https://doi.org/10.1016/j.cma.2023.116655}, issn = {0045-7825}, journal = {Computer Methods in Applied Mechanics and Engineering}, month = {02}, pages = 116655, title = {A new numerical mesoscopic scale one-domain approach solver for free fluid/porous medium interaction}, url = {https://www.sciencedirect.com/science/article/pii/S0045782523007788}, volume = 419, year = 2024 }

   Link

   https://www.sciencedirect.com/science/article/pii/S0045782523007788
3. Veyskarami, M., Bringedal, C., & Helmig, R. (2024). Modeling and Analysis of Droplet Evaporation at the Interface of a Coupled Free-Flow--Porous Medium System. Transport in Porous Media. https://doi.org/10.1007/s11242-024-02123-7
   • Abstract
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   Abstract

   Evaporation of droplets formed at the interface of a coupled free-flow–porous medium system enormously affects the exchange of mass, momentum, and energy between the two domains. In this work, we develop a model to describe multiple droplets’ evaporation at the interface, in which new sets of coupling conditions including the evaporating droplets are developed to describe the interactions between the free flow and the porous medium. Employing pore-network modeling to describe the porous medium, we take the exchanges occurring on the droplet–pore and droplet–free-flow interfaces into account. In this model, we describe the droplet evaporation as a diffusion-driven process, where vapor from the droplet surface diffuses into the surrounding free flow due to the concentration gradient. To validate the model, we compare the simulation results for the evaporation of a single droplet in a channel with experimental data, demonstrating that our model accurately describes the evaporation process. Then, we examine the impact of free-flow and porous medium properties on droplet evaporation. The results show that, among other factors, velocity and relative humidity in the free-flow domain, as well as pore temperature in the porous medium, play key roles in the droplet evaporation process.

   BibTeX

   @article{veyskarami_modeling_2024, abstract = {Evaporation of droplets formed at the interface of a coupled free-flow–porous medium system enormously affects the exchange of mass, momentum, and energy between the two domains. In this work, we develop a model to describe multiple droplets’ evaporation at the interface, in which new sets of coupling conditions including the evaporating droplets are developed to describe the interactions between the free flow and the porous medium. Employing pore-network modeling to describe the porous medium, we take the exchanges occurring on the droplet–pore and droplet–free-flow interfaces into account. In this model, we describe the droplet evaporation as a diffusion-driven process, where vapor from the droplet surface diffuses into the surrounding free flow due to the concentration gradient. To validate the model, we compare the simulation results for the evaporation of a single droplet in a channel with experimental data, demonstrating that our model accurately describes the evaporation process. Then, we examine the impact of free-flow and porous medium properties on droplet evaporation. The results show that, among other factors, velocity and relative humidity in the free-flow domain, as well as pore temperature in the porous medium, play key roles in the droplet evaporation process.}, author = {Veyskarami, Maziar and Bringedal, Carina and Helmig, Rainer}, doi = {10.1007/s11242-024-02123-7}, issn = {1573-1634}, journal = {Transport in Porous Media}, month = {10}, title = {Modeling and Analysis of Droplet Evaporation at the Interface of a Coupled Free-Flow--Porous Medium System}, url = {https://doi.org/10.1007/s11242-024-02123-7}, year = 2024 }

   Link

   https://doi.org/10.1007/s11242-024-02123-7
4. Schneider, J., Kiemle, S., Heck, K., Rothfuss, Y., Braud, I., Helmig, R., & Vanderborght, J. (2024). Analysis of experimental and simulation data of evaporation-driven isotopic fractionation in unsaturated porous media. Vadose Zone Journal, 23(5), Article 5. https://doi.org/10.1002/vzj2.20363
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   Abstract

   Abstract Stable water isotopologs can add valuable information to the understanding of evaporation processes. The identification of the evaporation front from isotopolog concentration depth profiles under very dry soil conditions is of particular interest. We compared two different models that describe isotopolog transport in a drying unsaturated porous medium: SiSPAT-Isotope and DuMux. In DuMux, the medium can dry out completely whereas in SiSPAT-Isotope, drying is limited to the residual water saturation. We evaluated the impact of residual water saturation on simulated isotopic concentration. For a low residual water saturation, both models simulated similar isotopolog concentrations. For high residual water saturation, SiSPAT-Isotope simulated considerably lower concentrations than DuMux. This is attributed to the buffering of changes in isotopolog concentrations by the residual water in SiSPAT-Isotope and an additional enrichment due to evaporation of residual water in DuMux. Additionally, we present a comparison between high-frequency experimental data and model simulations. We found that diffusive transport processes in the laminar boundary layer and in the dried-out surface soil layer need to be represented correctly to reproduce the observed downward movement of the evaporation front and the associated peak of isotopolog enrichment. Artificially increasing the boundary layer thickness to reproduce a decrease in evaporation rate leads to incorrect simulation of the location of the evaporation front and isotopolog concentration profile.

   BibTeX

   @article{https://doi.org/10.1002/vzj2.20363, abstract = {Abstract Stable water isotopologs can add valuable information to the understanding of evaporation processes. The identification of the evaporation front from isotopolog concentration depth profiles under very dry soil conditions is of particular interest. We compared two different models that describe isotopolog transport in a drying unsaturated porous medium: SiSPAT-Isotope and DuMux. In DuMux, the medium can dry out completely whereas in SiSPAT-Isotope, drying is limited to the residual water saturation. We evaluated the impact of residual water saturation on simulated isotopic concentration. For a low residual water saturation, both models simulated similar isotopolog concentrations. For high residual water saturation, SiSPAT-Isotope simulated considerably lower concentrations than DuMux. This is attributed to the buffering of changes in isotopolog concentrations by the residual water in SiSPAT-Isotope and an additional enrichment due to evaporation of residual water in DuMux. Additionally, we present a comparison between high-frequency experimental data and model simulations. We found that diffusive transport processes in the laminar boundary layer and in the dried-out surface soil layer need to be represented correctly to reproduce the observed downward movement of the evaporation front and the associated peak of isotopolog enrichment. Artificially increasing the boundary layer thickness to reproduce a decrease in evaporation rate leads to incorrect simulation of the location of the evaporation front and isotopolog concentration profile.}, author = {Schneider, Jana and Kiemle, Stefanie and Heck, Katharina and Rothfuss, Youri and Braud, Isabelle and Helmig, Rainer and Vanderborght, Jan}, doi = {https://doi.org/10.1002/vzj2.20363}, eprint = {https://acsess.onlinelibrary.wiley.com/doi/pdf/10.1002/vzj2.20363}, journal = {Vadose Zone Journal}, month = {07}, number = 5, pages = {e20363}, title = {Analysis of experimental and simulation data of evaporation-driven isotopic fractionation in unsaturated porous media}, url = {https://acsess.onlinelibrary.wiley.com/doi/abs/10.1002/vzj2.20363}, volume = 23, year = 2024 }

   Link

   https://acsess.onlinelibrary.wiley.com/doi/abs/10.1002/vzj2.20363
5. Schollenberger, T., von Wolff, L., Bringedal, C., Pop, I. S., Rohde, C., & Helmig, R. (2024). Investigation of Different Throat Concepts for Precipitation Processes in Saturated Pore-Network Models. Transport in Porous Media, 151(14), Article 14. https://doi.org/10.1007/s11242-024-02125-5
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   Abstract

   The development of reliable mathematical models and numerical discretization methods is important for the understanding of salt precipitation in porous media, which is relevant for environmental problems like soil salinization. Models on the pore scale are necessary to represent local heterogeneities in precipitation and to include the influence of solution-air-solid interfaces. A pore-network model for saturated flow, which includes the precipitation reaction of salt, is presented. It is implemented in the open-source simulator DuMuX. In this paper, we restrict ourselves to one-phase flow as a first step. Since the throat transmissibilities determine the flow behaviour in the pore network, different concepts for the decreasing throat transmissibility due to precipitation are investigated. We consider four concepts for the amount of precipitation in the throats. Three concepts use information from the adjacent pore bodies, and one employs a pore-throat model obtained by averaging the resolved pore-scale model in a thin-tube. They lead to different permeability developments, which are caused by the different distribution of the precipitate between the pore bodies and throats. We additionally apply two different concepts for the calculation of the transmissibility. One obtains the precipitate distribution from analytical assumptions, the other from a geometric minimization principle using a phase-field evolution equation. The two concepts do not show substantial differences for the permeability development as long as simple pore-throat geometries are used. Finally, advantages and disadvantages of the concepts are discussed in the context of the considered physical problem and a reasonable effort for the implementation and computational costs.

   BibTeX

   @article{schollenberger_investigation_2024, abstract = {The development of reliable mathematical models and numerical discretization methods is important for the understanding of salt precipitation in porous media, which is relevant for environmental problems like soil salinization. Models on the pore scale are necessary to represent local heterogeneities in precipitation and to include the influence of solution-air-solid interfaces. A pore-network model for saturated flow, which includes the precipitation reaction of salt, is presented. It is implemented in the open-source simulator DuMuX. In this paper, we restrict ourselves to one-phase flow as a first step. Since the throat transmissibilities determine the flow behaviour in the pore network, different concepts for the decreasing throat transmissibility due to precipitation are investigated. We consider four concepts for the amount of precipitation in the throats. Three concepts use information from the adjacent pore bodies, and one employs a pore-throat model obtained by averaging the resolved pore-scale model in a thin-tube. They lead to different permeability developments, which are caused by the different distribution of the precipitate between the pore bodies and throats. We additionally apply two different concepts for the calculation of the transmissibility. One obtains the precipitate distribution from analytical assumptions, the other from a geometric minimization principle using a phase-field evolution equation. The two concepts do not show substantial differences for the permeability development as long as simple pore-throat geometries are used. Finally, advantages and disadvantages of the concepts are discussed in the context of the considered physical problem and a reasonable effort for the implementation and computational costs.}, author = {Schollenberger, Theresa and von Wolff, Lars and Bringedal, Carina and Pop, Iuliu Sorin and Rohde, Christian and Helmig, Rainer}, doi = {10.1007/s11242-024-02125-5}, issn = {1573-1634}, journal = {Transport in Porous Media}, month = {11}, number = 14, pages = {2647--2692}, title = {Investigation of Different Throat Concepts for Precipitation Processes in Saturated Pore-Network Models}, url = {https://doi.org/10.1007/s11242-024-02125-5}, volume = 151, year = 2024 }

   Link

   https://doi.org/10.1007/s11242-024-02125-5
6. Boon, W. M., Gläser, D., Helmig, R., Weishaupt, K., & Yotov, I. (2024). A mortar method for the coupled Stokes-Darcy problem using the MAC scheme for Stokes and mixed finite elements for Darcy. Computational Geosciences, 28(3), Article 3. https://doi.org/10.1007/s10596-023-10267-6
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   Abstract

   A discretization method with non-matching grids is proposed for the coupled Stokes-Darcy problem that uses a mortar variable at the interface to couple the marker and cell (MAC) method in the Stokes domain with the Raviart-Thomas mixed finite element pair in the Darcy domain. Due to this choice, the method conserves linear momentum and mass locally in the Stokes domain and exhibits local mass conservation in the Darcy domain. The MAC scheme is reformulated as a mixed finite element method on a staggered grid, which allows for the proposed scheme to be analyzed as a mortar mixed finite element method. We show that the discrete system is well-posed and derive a priori error estimates that indicate first order convergence in all variables. The system can be reduced to an interface problem concerning only the mortar variables, leading to a non-overlapping domain decomposition method. Numerical examples are presented to illustrate the theoretical results and the applicability of the method.

   BibTeX

   @article{boon_mortar_2024, abstract = {A discretization method with non-matching grids is proposed for the coupled Stokes-Darcy problem that uses a mortar variable at the interface to couple the marker and cell (MAC) method in the Stokes domain with the Raviart-Thomas mixed finite element pair in the Darcy domain. Due to this choice, the method conserves linear momentum and mass locally in the Stokes domain and exhibits local mass conservation in the Darcy domain. The MAC scheme is reformulated as a mixed finite element method on a staggered grid, which allows for the proposed scheme to be analyzed as a mortar mixed finite element method. We show that the discrete system is well-posed and derive a priori error estimates that indicate first order convergence in all variables. The system can be reduced to an interface problem concerning only the mortar variables, leading to a non-overlapping domain decomposition method. Numerical examples are presented to illustrate the theoretical results and the applicability of the method.}, author = {Boon, Wietse M. and Gläser, Dennis and Helmig, Rainer and Weishaupt, Kilian and Yotov, Ivan}, doi = {10.1007/s10596-023-10267-6}, issn = {1573-1499}, journal = {Computational Geosciences}, month = {06}, number = 3, pages = {413--430}, title = {A mortar method for the coupled Stokes-Darcy problem using the MAC scheme for Stokes and mixed finite elements for Darcy}, url = {https://doi.org/10.1007/s10596-023-10267-6}, volume = 28, year = 2024 }

   Link

   https://doi.org/10.1007/s10596-023-10267-6
7. Tatomir, A., Gao, H., Abdullah, H., Pötzl, C., Karadimitriou, N., Steeb, H., Licha, T., Class, H., Helmig, R., & Sauter, M. (2023). Estimation of Capillary-Associated NAPL-Water Interfacial Areas for Unconsolidated Porous Media by Kinetic Interface Sensitive (KIS) Tracer Method. Water Resources Research, 59(12), Article 12. https://doi.org/10.1029/2023WR035387
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   Abstract

   Abstract By employing kinetic interface sensitive (KIS) tracers, we investigate three different types of glass-bead materials and three natural porous media systems to quantitatively characterize the influence of the porous-medium grain-, pore-size and texture on the specific capillary-associated interfacial area (FIFA) between an organic liquid and water. By interpreting the breakthrough curves (BTCs) of the reaction product of the KIS tracer hydrolysis, we obtain a relation for the specific IFA and wetting phase saturation. The immiscible displacement process coupled with the reactive tracer transport across the fluid–fluid interface is simulated with a Darcy-scale numerical model. Linear relations between the specific capillary-associated FIFA and the inverse mean grain diameter can be established for measurements with glass beads and natural soils. We find that the grain size has minimal effect on the capillary-associated FIFA for unconsolidated porous media formed by glass beads. Conversely, for unconsolidated porous media formed by natural soils, the capillary-associated FIFA linearly increases with the inverse mean grain diameter, and it is much larger than that from glass beads. This indicates that the surface roughness and the irregular shape of the grains can cause the capillary-associated FIFA to increase. The results are also compared with the data collected from literature, measured with high resolution microtomography and partitioning tracer methods. Our study considerably expands the applicability range of the KIS tracers and enhances the confidence in the robustness of the method.

   BibTeX

   @article{https://doi.org/10.1029/2023WR035387, abstract = {Abstract By employing kinetic interface sensitive (KIS) tracers, we investigate three different types of glass-bead materials and three natural porous media systems to quantitatively characterize the influence of the porous-medium grain-, pore-size and texture on the specific capillary-associated interfacial area (FIFA) between an organic liquid and water. By interpreting the breakthrough curves (BTCs) of the reaction product of the KIS tracer hydrolysis, we obtain a relation for the specific IFA and wetting phase saturation. The immiscible displacement process coupled with the reactive tracer transport across the fluid–fluid interface is simulated with a Darcy-scale numerical model. Linear relations between the specific capillary-associated FIFA and the inverse mean grain diameter can be established for measurements with glass beads and natural soils. We find that the grain size has minimal effect on the capillary-associated FIFA for unconsolidated porous media formed by glass beads. Conversely, for unconsolidated porous media formed by natural soils, the capillary-associated FIFA linearly increases with the inverse mean grain diameter, and it is much larger than that from glass beads. This indicates that the surface roughness and the irregular shape of the grains can cause the capillary-associated FIFA to increase. The results are also compared with the data collected from literature, measured with high resolution microtomography and partitioning tracer methods. Our study considerably expands the applicability range of the KIS tracers and enhances the confidence in the robustness of the method.}, author = {Tatomir, Alexandru and Gao, Huhao and Abdullah, Hiwa and Pötzl, Christopher and Karadimitriou, Nikolaos and Steeb, Holger and Licha, Tobias and Class, Holger and Helmig, Rainer and Sauter, Martin}, doi = {https://doi.org/10.1029/2023WR035387}, eprint = {https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2023WR035387}, journal = {Water Resources Research}, month = {12}, note = {e2023WR035387 2023WR035387}, number = 12, pages = {e2023WR035387}, title = {Estimation of Capillary-Associated NAPL-Water Interfacial Areas for Unconsolidated Porous Media by Kinetic Interface Sensitive (KIS) Tracer Method}, url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2023WR035387}, volume = 59, year = 2023 }

   Link

   https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2023WR035387
8. Veyskarami, M., Michalkowski, C., Bringedal, C., & Helmig, R. (2023). Droplet Formation, Growth and Detachment at the Interface of a Coupled Free-FLow--Porous Medium System: A New Model Development and Comparison. Transport in Porous Media, 149, 389–419. https://doi.org/10.1007/s11242-023-01944-2
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   BibTeX

   @article{veyskarami2023droplet, author = {Veyskarami, Maziar and Michalkowski, Cynthia and Bringedal, Carina and Helmig, Rainer}, doi = {10.1007/s11242-023-01944-2}, journal = {Transport in Porous Media}, month = {05}, pages = {389–419}, publisher = {Springer}, title = {Droplet Formation, Growth and Detachment at the Interface of a Coupled Free-FLow--Porous Medium System: A New Model Development and Comparison}, url = {https://link.springer.com/article/10.1007/s11242-023-01944-2}, volume = 149, year = 2023 }

   Link

   https://link.springer.com/article/10.1007/s11242-023-01944-2
9. Wu, H., Veyskarami, M., Schneider, M., & Helmig, R. (2023). A New Fully Implicit Two-Phase Pore-Network Model by Utilizing Regularization Strategies. Transport in Porous Media. https://doi.org/10.1007/s11242-023-02031-2
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   Abstract

   In this paper, we address the expensive computational cost resulting from limited time-step sizes during numerical simulations of two-phase flow in porous media using dynamic pore-network models. To overcome this issue, we propose a numerical method for dynamic pore-network models using a fully implicit approach. The proposed method introduces a regularization strategy considering the historical fluid configuration at the pore throat, which smooths the discontinuities in local conductivity caused by invasion and snap-off events. The results demonstrate the superiority of the proposed method in terms of accuracy, efficiency and consistency in comparison with other numerical schemes. With similar computational cost, determined by time-step sizes and number of Newton iterations, the developed method in this work yields more accurate results compared to similar schemes presented in the literature. Additionally, our results highlight the enhanced robustness of the our scheme, as it exhibits reduced sensitivity to variations in time-step sizes.

   BibTeX

   @article{wu_new_2023, abstract = {In this paper, we address the expensive computational cost resulting from limited time-step sizes during numerical simulations of two-phase flow in porous media using dynamic pore-network models. To overcome this issue, we propose a numerical method for dynamic pore-network models using a fully implicit approach. The proposed method introduces a regularization strategy considering the historical fluid configuration at the pore throat, which smooths the discontinuities in local conductivity caused by invasion and snap-off events. The results demonstrate the superiority of the proposed method in terms of accuracy, efficiency and consistency in comparison with other numerical schemes. With similar computational cost, determined by time-step sizes and number of Newton iterations, the developed method in this work yields more accurate results compared to similar schemes presented in the literature. Additionally, our results highlight the enhanced robustness of the our scheme, as it exhibits reduced sensitivity to variations in time-step sizes.}, author = {Wu, Hanchuan and Veyskarami, Maziar and Schneider, Martin and Helmig, Rainer}, doi = {10.1007/s11242-023-02031-2}, issn = {1573-1634}, journal = {Transport in Porous Media}, month = {10}, title = {A New Fully Implicit Two-Phase Pore-Network Model by Utilizing Regularization Strategies}, url = {https://doi.org/10.1007/s11242-023-02031-2}, year = 2023 }

   Link

   https://doi.org/10.1007/s11242-023-02031-2
10. Kiemle, S., Heck, K., Coltman, E., & Helmig, R. (2023). Stable Water Isotopologue Fractionation During Soil-Water Evaporation: Analysis Using a Coupled Soil-Atmosphere Model. Water Resources Research, 59(2), Article 2. https://doi.org/10.1029/2022WR032385
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    Abstract

    Abstract The atmosphere-soil system forms a highly coupled system, which makes key processes such as evaporation complex to analyze as the mass, energy, and momentum transfer is influenced by both domains. To enhance the understanding of evaporation processes from soils, stable water isotopologues are suitable tools to trace water movement within these systems as heavier isotopologues enrich in the residual liquid phase. Due to the complex coupled processes involved in simulating soil-water evaporation accurately, quantifying fractionation during flow and transport processes at the soil-atmosphere interface remains an open research area. In this work, we present a multi-phase multi-component transport model that resolves flow through the near-surface atmosphere and the soil, and models transport and fractionation of the stable water isotopologues using the numerical simulation environment DuMux. Using this coupled model, we simulate transport and fractionation processes of stable water isotopologues in soils and the atmosphere by solving compositional flow equations and by using suitable coupling conditions at the soil-atmosphere interface instead of commonly used parameterization. In a series of examples of evaporation from bare soil, the transport and distribution of stable water isotopologues are evaluated numerically with varied conditions and assumptions, including different atmospheric conditions (turbulent/laminar flow, wind speed) and their impact on the spatial and temporal distribution of the isotopic composition. Building on these results, we observed how the enrichment of the isotopologues in soil is linked with the different stages of the evaporation process. A qualitative study is conducted to verify single fractionation processes in our approach.

    BibTeX

    @article{https://doi.org/10.1029/2022WR032385, abstract = {Abstract The atmosphere-soil system forms a highly coupled system, which makes key processes such as evaporation complex to analyze as the mass, energy, and momentum transfer is influenced by both domains. To enhance the understanding of evaporation processes from soils, stable water isotopologues are suitable tools to trace water movement within these systems as heavier isotopologues enrich in the residual liquid phase. Due to the complex coupled processes involved in simulating soil-water evaporation accurately, quantifying fractionation during flow and transport processes at the soil-atmosphere interface remains an open research area. In this work, we present a multi-phase multi-component transport model that resolves flow through the near-surface atmosphere and the soil, and models transport and fractionation of the stable water isotopologues using the numerical simulation environment DuMux. Using this coupled model, we simulate transport and fractionation processes of stable water isotopologues in soils and the atmosphere by solving compositional flow equations and by using suitable coupling conditions at the soil-atmosphere interface instead of commonly used parameterization. In a series of examples of evaporation from bare soil, the transport and distribution of stable water isotopologues are evaluated numerically with varied conditions and assumptions, including different atmospheric conditions (turbulent/laminar flow, wind speed) and their impact on the spatial and temporal distribution of the isotopic composition. Building on these results, we observed how the enrichment of the isotopologues in soil is linked with the different stages of the evaporation process. A qualitative study is conducted to verify single fractionation processes in our approach.}, author = {Kiemle, Stefanie and Heck, Katharina and Coltman, Edward and Helmig, Rainer}, doi = {https://doi.org/10.1029/2022WR032385}, eprint = {https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2022WR032385}, issn = {1944-7973}, journal = {Water Resources Research}, month = {02}, note = {e2022WR032385 2022WR032385}, number = 2, pages = {e2022WR032385}, publisher = {American Geophysical Union (AGU)}, title = {Stable Water Isotopologue Fractionation During Soil-Water Evaporation: Analysis Using a Coupled Soil-Atmosphere Model}, url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2022WR032385}, volume = 59, year = 2023 }

    Link

    https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2022WR032385
11. Ackermann, S., Fest-Santini, S., Veyskarami, M., Helmig, R., & Santini, M. (2023). Experimental validation of a coupling concept for drop formation and growth onto porous materials by high-resolution X-ray imaging technique. International Journal of Multiphase Flow, 160. https://doi.org/10.1016/j.ijmultiphaseflow.2022.104371
    • Abstract
    • BibTeX
    • Link

    Abstract

    Droplets formed on the hydrophobic surface of a porous medium exposed to a cross-flowing gas stream have a strong influence on the mass, momentum, and energy exchange across the porous interface, being of importance in several physical systems and engineering applications, like fuel cells. However, the fluid displacement front is highly complex at the pore-scale, since it is characterized by the surface wettability and a contact angle variation along the triple line. Furthermore, the droplet formation is affected by the pore geometry and the surface wettability. These result in a challenging multi-phase scenario with controversial literature, and few studies consider the detailed mechanism of droplet formation on the surface of the porous medium. In this work, two multi-scale simulations for the emerging water droplet from a single hydrophobic capillary pore opening into the gas phase are validated by a benchmark experiment with the help of a high-resolution X-ray imaging technique to characterize the droplet growing. A three-domain approach (gaseous free flow, interface and porous medium, FIP) was compared with a two-domain approach (based on a free-flow and the porous medium, FP). Whereas the three-domain approach introduces two sets of coupling conditions, one for the free flow-interface and one for the interface-porous medium, the two-domain approach introduces only one set of coupling connections for describing the interaction between the domains. In both approaches, droplet formation and growth alter the coupling conditions between the domains. While the FIP approach treats the porous medium as a continuous matter, it is resolved discretely with the help of a pore network in the FP approach. Both approaches show good agreements with the experimental observations and high correspondences for the drop volume, radii and contact angle evolution. The proposed models provide a base for future developments and help to gain a better insight about the impact of the droplet formation on the interface in a coupled free flow-porous medium system.

    BibTeX

    @article{paper-2023-ackermann-experimentalvalidation, abstract = {Droplets formed on the hydrophobic surface of a porous medium exposed to a cross-flowing gas stream have a strong influence on the mass, momentum, and energy exchange across the porous interface, being of importance in several physical systems and engineering applications, like fuel cells. However, the fluid displacement front is highly complex at the pore-scale, since it is characterized by the surface wettability and a contact angle variation along the triple line. Furthermore, the droplet formation is affected by the pore geometry and the surface wettability. These result in a challenging multi-phase scenario with controversial literature, and few studies consider the detailed mechanism of droplet formation on the surface of the porous medium. In this work, two multi-scale simulations for the emerging water droplet from a single hydrophobic capillary pore opening into the gas phase are validated by a benchmark experiment with the help of a high-resolution X-ray imaging technique to characterize the droplet growing. A three-domain approach (gaseous free flow, interface and porous medium, FIP) was compared with a two-domain approach (based on a free-flow and the porous medium, FP). Whereas the three-domain approach introduces two sets of coupling conditions, one for the free flow-interface and one for the interface-porous medium, the two-domain approach introduces only one set of coupling connections for describing the interaction between the domains. In both approaches, droplet formation and growth alter the coupling conditions between the domains. While the FIP approach treats the porous medium as a continuous matter, it is resolved discretely with the help of a pore network in the FP approach. Both approaches show good agreements with the experimental observations and high correspondences for the drop volume, radii and contact angle evolution. The proposed models provide a base for future developments and help to gain a better insight about the impact of the droplet formation on the interface in a coupled free flow-porous medium system.}, author = {Ackermann, Sina and Fest-Santini, Stephanie and Veyskarami, Maziar and Helmig, Rainer and Santini, Maurizio}, doi = {https://doi.org/10.1016/j.ijmultiphaseflow.2022.104371}, journal = {International Journal of Multiphase Flow}, month = {01}, page = {104371}, title = {Experimental validation of a coupling concept for drop formation and growth onto porous materials by high-resolution X-ray imaging technique}, url = {https://www.sciencedirect.com/science/article/pii/S0301932222003305}, volume = 160, year = 2023 }

    Link

    https://www.sciencedirect.com/science/article/pii/S0301932222003305
12. Schneider, M., Gläser, D., Weishaupt, K., Coltman, E., Flemisch, B., & Helmig, R. (2023). Coupling staggered-grid and vertex-centered finite-volume methods for coupled porous-medium free-flow problems. Journal of Computational Physics, 482, 112042. https://doi.org/10.1016/j.jcp.2023.112042
    • Abstract
    • BibTeX
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    Abstract

    A new discretization approach for coupled free and porous-medium flows is introduced, which uses a finite-volume staggered-grid method for the discretization of the Navier-Stokes equations in the free-flow subdomain, while a vertex-centered finite-volume method is employed in the porous medium. The latter allows for the use of unstructured grids to discretize the porous medium, and the presented method is capable of handling non-matching grids at the interface. Moreover, the basis functions of the vertex-centered finite-volume method, with their degrees of freedom located at the interface, allow for an accurate evaluation of the coupling terms and of additional nonlinear velocity-dependent terms in the porous medium. The available advantages of this coupling method are investigated in a series of tests: a convergence test for various grid types, an evaluation of the implementation of the coupling conditions, and an example using the velocity-dependent Forchheimer term in the porous-medium subdomain.

    BibTeX

    @article{SCHNEIDER2023112042, abstract = {A new discretization approach for coupled free and porous-medium flows is introduced, which uses a finite-volume staggered-grid method for the discretization of the Navier-Stokes equations in the free-flow subdomain, while a vertex-centered finite-volume method is employed in the porous medium. The latter allows for the use of unstructured grids to discretize the porous medium, and the presented method is capable of handling non-matching grids at the interface. Moreover, the basis functions of the vertex-centered finite-volume method, with their degrees of freedom located at the interface, allow for an accurate evaluation of the coupling terms and of additional nonlinear velocity-dependent terms in the porous medium. The available advantages of this coupling method are investigated in a series of tests: a convergence test for various grid types, an evaluation of the implementation of the coupling conditions, and an example using the velocity-dependent Forchheimer term in the porous-medium subdomain.}, author = {Schneider, Martin and Gläser, Dennis and Weishaupt, Kilian and Coltman, Edward and Flemisch, Bernd and Helmig, Rainer}, doi = {https://doi.org/10.1016/j.jcp.2023.112042}, issn = {0021-9991}, journal = {Journal of Computational Physics}, month = {07}, pages = 112042, title = {Coupling staggered-grid and vertex-centered finite-volume methods for coupled porous-medium free-flow problems}, url = {https://www.sciencedirect.com/science/article/pii/S0021999123001377}, volume = 482, year = 2023 }

    Link

    https://www.sciencedirect.com/science/article/pii/S0021999123001377
13. Boon, W. M., Gläser, D., Helmig, R., & Yotov, I. (2023). Flux-mortar mixed finite element methods with multipoint flux approximation. Computer Methods in Applied Mechanics and Engineering, 405, 115870. https://doi.org/10.1016/j.cma.2022.115870
    • Abstract
    • BibTeX
    • Link

    Abstract

    The flux-mortar mixed finite element method was recently developed in Boon et al. (2022) for a general class of domain decomposition saddle point problems on non-matching grids. In this work we develop the method for Darcy flow using the multipoint flux approximation as the subdomain discretization. The subdomain problems involve solving positive definite cell-centered pressure systems. The normal flux on the subdomain interfaces is the mortar coupling variable, which plays the role of a Lagrange multiplier to impose weakly continuity of pressure. We present well-posedness and error analysis based on reformulating the method as a mixed finite element method with a quadrature rule. We develop a non-overlapping domain decomposition algorithm for the solution of the resulting algebraic system that reduces it to an interface problem for the flux-mortar, as well as an efficient interface preconditioner. A series of numerical experiments is presented illustrating the performance of the method on general grids, including applications to flow in complex porous media.

    BibTeX

    @article{paper-2023-boon-flux-mortar, abstract = {The flux-mortar mixed finite element method was recently developed in Boon et al. (2022) for a general class of domain decomposition saddle point problems on non-matching grids. In this work we develop the method for Darcy flow using the multipoint flux approximation as the subdomain discretization. The subdomain problems involve solving positive definite cell-centered pressure systems. The normal flux on the subdomain interfaces is the mortar coupling variable, which plays the role of a Lagrange multiplier to impose weakly continuity of pressure. We present well-posedness and error analysis based on reformulating the method as a mixed finite element method with a quadrature rule. We develop a non-overlapping domain decomposition algorithm for the solution of the resulting algebraic system that reduces it to an interface problem for the flux-mortar, as well as an efficient interface preconditioner. A series of numerical experiments is presented illustrating the performance of the method on general grids, including applications to flow in complex porous media.}, author = {Boon, Wietse M. and Gläser, Dennis and Helmig, Rainer and Yotov, Ivan}, doi = {10.1016/j.cma.2022.115870}, issn = {0045-7825}, journal = {Computer Methods in Applied Mechanics and Engineering}, pages = 115870, title = {Flux-mortar mixed finite element methods with multipoint flux approximation}, url = {https://www.sciencedirect.com/science/article/pii/S004578252200826X}, volume = 405, year = 2023 }

    Link

    https://www.sciencedirect.com/science/article/pii/S004578252200826X
14. Michalkowski, C., Weishaupt, K., Schleper, V., & Helmig, R. (2022). Modeling of Two Phase Flow in a Hydrophobic Porous Medium Interacting with a Hydrophilic Structure. Transport in Porous Media, 144(2), Article 2. https://doi.org/10.1007/s11242-022-01816-1
    • Abstract
    • BibTeX
    • Link

    Abstract

    Fluid flow through layered materials with different wetting behavior is observed in a wide range of applications in biological, environmental and technical systems. Therefore, it is necessary to understand the occuring transport mechanisms of the fluids at the interface between the layered constituents. Of special interest is the water transport in polymer electrolyte membrane fuel cells. Here, it is necessary to understand the transport mechanisms of water throughout the cell constituents especially on the cathode side, where the excess water has to be removed. This is crucial to choose optimal operating conditions and improve the overall cell performance. Pore-scale modeling of gas diffusion layers (GDLs) and gas distributor has been established as a favorable technique to investigate the ongoing processes. Investigating the interface between the hydrophobic porous GDL and the hydrophilic gas distributor, a particular challenge is the combination and interaction of the different material structures and wetting properties at the interface and its influence on the flow. In this paper, a modeling approach is presented which captures the influence of a hydrophilic domain on the flow in a hydrophobic porous domain at the interface between the two domains. A pore-network model is used as the basis of the developed concept which is extended to allow the modeling of mixed-wet interactions at the interface. The functionality of the model is demonstrated using basic example configurations with one and several interface pores and it is applied to a realistic GDL representation in contact with a channel-land structured gas distributor.

    BibTeX

    @article{michalkowski_modeling_2022, abstract = {Fluid flow through layered materials with different wetting behavior is observed in a wide range of applications in biological, environmental and technical systems. Therefore, it is necessary to understand the occuring transport mechanisms of the fluids at the interface between the layered constituents. Of special interest is the water transport in polymer electrolyte membrane fuel cells. Here, it is necessary to understand the transport mechanisms of water throughout the cell constituents especially on the cathode side, where the excess water has to be removed. This is crucial to choose optimal operating conditions and improve the overall cell performance. Pore-scale modeling of gas diffusion layers (GDLs) and gas distributor has been established as a favorable technique to investigate the ongoing processes. Investigating the interface between the hydrophobic porous GDL and the hydrophilic gas distributor, a particular challenge is the combination and interaction of the different material structures and wetting properties at the interface and its influence on the flow. In this paper, a modeling approach is presented which captures the influence of a hydrophilic domain on the flow in a hydrophobic porous domain at the interface between the two domains. A pore-network model is used as the basis of the developed concept which is extended to allow the modeling of mixed-wet interactions at the interface. The functionality of the model is demonstrated using basic example configurations with one and several interface pores and it is applied to a realistic GDL representation in contact with a channel-land structured gas distributor.}, author = {Michalkowski, Cynthia and Weishaupt, Kilian and Schleper, Veronika and Helmig, Rainer}, doi = {10.1007/s11242-022-01816-1}, issn = {1573-1634}, journal = {Transport in Porous Media}, month = {09}, number = 2, pages = {481--506}, title = {Modeling of Two Phase Flow in a Hydrophobic Porous Medium Interacting with a Hydrophilic Structure}, url = {https://doi.org/10.1007/s11242-022-01816-1}, volume = 144, year = 2022 }

    Link

    https://doi.org/10.1007/s11242-022-01816-1
15. Bringedal, C., Schollenberger, T., Pieters, G. J. M., van Duijn, C. J., & Helmig, R. (2022). Evaporation-Driven Density Instabilities in Saturated Porous Media. Transport in Porous Media, 143(2), Article 2. https://doi.org/10.1007/s11242-022-01772-w
    • Abstract
    • BibTeX
    • Link

    Abstract

    Soil salinization is a major cause of soil degradation and hampers plant growth. For soils saturated with saline water, the evaporation of water induces accumulation of salt near the top of the soil. The remaining liquid gets an increasingly larger density due to the accumulation of salt, giving a gravitationally unstable situation, where instabilities in the form of fingers can form. These fingers can, hence, lead to a net downward transport of salt. We here investigate the appearance of these fingers through a linear stability analysis and through numerical simulations. The linear stability analysis gives criteria for onset of instabilities for a large range of parameters. Simulations using a set of parameters give information also about the development of the fingers after onset. With this knowledge, we can predict whether and when the instabilities occur, and their effect on the salt concentration development near the top boundary.

    BibTeX

    @article{bringedal_evaporation-driven_2022, abstract = {Soil salinization is a major cause of soil degradation and hampers plant growth. For soils saturated with saline water, the evaporation of water induces accumulation of salt near the top of the soil. The remaining liquid gets an increasingly larger density due to the accumulation of salt, giving a gravitationally unstable situation, where instabilities in the form of fingers can form. These fingers can, hence, lead to a net downward transport of salt. We here investigate the appearance of these fingers through a linear stability analysis and through numerical simulations. The linear stability analysis gives criteria for onset of instabilities for a large range of parameters. Simulations using a set of parameters give information also about the development of the fingers after onset. With this knowledge, we can predict whether and when the instabilities occur, and their effect on the salt concentration development near the top boundary.}, author = {Bringedal, Carina and Schollenberger, Theresa and Pieters, G. J. M. and van Duijn, C. J. and Helmig, Rainer}, doi = {10.1007/s11242-022-01772-w}, issn = {1573-1634}, journal = {Transport in Porous Media}, language = {en}, month = {06}, number = 2, pages = {297--341}, title = {Evaporation-{Driven} {Density} {Instabilities} in {Saturated} {Porous} {Media}}, url = {https://doi.org/10.1007/s11242-022-01772-w}, urldate = {2022-07-08}, volume = 143, year = 2022 }

    Link

    https://doi.org/10.1007/s11242-022-01772-w
16. Boon, W. M., Gläser, D., Helmig, R., & Yotov, I. (2022). Flux-Mortar Mixed Finite Element Methods on NonMatching Grids. SIAM Journal on Numerical Analysis, 60(3), Article 3. https://doi.org/10.1137/20M1361407
    • Abstract
    • BibTeX
    • Link

    Abstract

    We investigate a mortar technique for mixed finite element approximations of a class of domain decomposition saddle point problems on nonmatching grids in which the variable associated with the essential boundary condition, referred to as flux, is chosen as the coupling variable. It plays the role of a Lagrange multiplier to impose weakly continuity of the variable associated with the natural boundary condition. The flux-mortar variable is incorporated with the use of a discrete extension operator. We present well-posedness and error analysis in an abstract setting under a set of suitable assumptions, followed by a nonoverlapping domain decomposition algorithm that reduces the global problem to a positive definite interface problem. The abstract theory is illustrated for Darcy flow, where the normal flux is the mortar variable used to impose continuity of pressure, and for Stokes flow, where the velocity vector is the mortar variable used to impose continuity of normal stress. In both examples, suitable discrete extension operators are developed and the assumptions from the abstract theory are verified. Numerical studies illustrating the theoretical results are presented for Darcy flow.

    BibTeX

    @article{doi:10.1137/20M1361407, abstract = { We investigate a mortar technique for mixed finite element approximations of a class of domain decomposition saddle point problems on nonmatching grids in which the variable associated with the essential boundary condition, referred to as flux, is chosen as the coupling variable. It plays the role of a Lagrange multiplier to impose weakly continuity of the variable associated with the natural boundary condition. The flux-mortar variable is incorporated with the use of a discrete extension operator. We present well-posedness and error analysis in an abstract setting under a set of suitable assumptions, followed by a nonoverlapping domain decomposition algorithm that reduces the global problem to a positive definite interface problem. The abstract theory is illustrated for Darcy flow, where the normal flux is the mortar variable used to impose continuity of pressure, and for Stokes flow, where the velocity vector is the mortar variable used to impose continuity of normal stress. In both examples, suitable discrete extension operators are developed and the assumptions from the abstract theory are verified. Numerical studies illustrating the theoretical results are presented for Darcy flow. }, author = {Boon, Wietse M. and Gläser, Dennis and Helmig, Rainer and Yotov, Ivan}, doi = {10.1137/20M1361407}, eprint = {https://doi.org/10.1137/20M1361407}, journal = {SIAM Journal on Numerical Analysis}, month = {05}, number = 3, pages = {1193-1225}, title = {Flux-Mortar Mixed Finite Element Methods on NonMatching Grids}, url = {https://doi.org/10.1137/20M1361407}, volume = 60, year = 2022 }

    Link

    https://doi.org/10.1137/20M1361407
17. Younes, A., Hoteit, H., Helmig, R., & Fahs, M. (2022). A robust upwind mixed hybrid finite element method  for transport in variably saturated porous media. Hydrology and Earth System Sciences, 26(20), Article 20. https://doi.org/10.5194/hess-26-5227-2022
    • BibTeX
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    BibTeX

    @article{Younes2022, author = {Younes, Anis and Hoteit, Hussein and Helmig, Rainer and Fahs, Marwan}, doi = {10.5194/hess-26-5227-2022}, issn = {1607-7938}, journal = {Hydrology and Earth System Sciences}, month = {10}, number = 20, pages = {5227–5239}, publisher = {Copernicus GmbH}, title = {A robust upwind mixed hybrid finite element method for transport in variably saturated porous media}, url = {http://dx.doi.org/10.5194/hess-26-5227-2022}, volume = 26, year = 2022 }

    Link

    http://dx.doi.org/10.5194/hess-26-5227-2022
18. Tsinober, A., Rosenzweig, R., Class, H., Helmig, R., & Shavit, U. (2022). The Role of Mixed Convection and Hydrodynamic Dispersion During CO2 Dissolution in Saline Aquifers: A Numerical Study. Water Resources Research, 58(3), Article 3. https://doi.org/10.1029/2021WR030494
    • Abstract
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    Abstract

    Abstract Dissolution trapping plays a significant role in CO2 geological storage. When CO2 dissolves in aquifer brines, the aqueous solution is heavier than the underlying resident brine. This results in convective instability in the form of CO2-rich fingers, which accelerates dissolution. It was recently shown that background flow affects CO2 dissolution by suppressing the development of convective fingers. However, there was a discrepancy between computational results and measurements, with the computational results demonstrating a decrease in the dissolution rate and the laboratory measurements showing no significant effect. Here, we attempted to understand this difference by exploring the relations between the transport mechanisms that facilitate convective mixing. We investigated the role of background flow by using numerical simulations that were validated by laboratory measurements and analytical solutions. Simulations were generated for the same porous medium and fluid pair used in the experiments, keeping the Rayleigh number constant, while changing the background velocity and the Peclet number. Studying the flux components revealed three distinct regimes characterized by the Peclet to Rayleigh ratio Pe/Ra. When Pe/Ra < 0.77, natural convection dominated, and dissolution remained approximately constant. When the background flow was large (Pe/Ra > 2), dissolution was controlled by pure forced convection and increased with Pe/Ra. In the intermediate range (0.77 < Pe/Ra < 2), both natural convection and forced convection were important.

    BibTeX

    @article{https://doi.org/10.1029/2021WR030494, abstract = {Abstract Dissolution trapping plays a significant role in CO2 geological storage. When CO2 dissolves in aquifer brines, the aqueous solution is heavier than the underlying resident brine. This results in convective instability in the form of CO2-rich fingers, which accelerates dissolution. It was recently shown that background flow affects CO2 dissolution by suppressing the development of convective fingers. However, there was a discrepancy between computational results and measurements, with the computational results demonstrating a decrease in the dissolution rate and the laboratory measurements showing no significant effect. Here, we attempted to understand this difference by exploring the relations between the transport mechanisms that facilitate convective mixing. We investigated the role of background flow by using numerical simulations that were validated by laboratory measurements and analytical solutions. Simulations were generated for the same porous medium and fluid pair used in the experiments, keeping the Rayleigh number constant, while changing the background velocity and the Peclet number. Studying the flux components revealed three distinct regimes characterized by the Peclet to Rayleigh ratio Pe/Ra. When Pe/Ra < 0.77, natural convection dominated, and dissolution remained approximately constant. When the background flow was large (Pe/Ra > 2), dissolution was controlled by pure forced convection and increased with Pe/Ra. In the intermediate range (0.77 < Pe/Ra < 2), both natural convection and forced convection were important.}, author = {Tsinober, Avihai and Rosenzweig, Ravid and Class, Holger and Helmig, Rainer and Shavit, Uri}, doi = {https://doi.org/10.1029/2021WR030494}, eprint = {https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2021WR030494}, journal = {Water Resources Research}, month = {03}, note = {e2021WR030494 2021WR030494}, number = 3, pages = {e2021WR030494}, title = {The Role of Mixed Convection and Hydrodynamic Dispersion During CO2 Dissolution in Saline Aquifers: A Numerical Study}, url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2021WR030494}, volume = 58, year = 2022 }

    Link

    https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2021WR030494
19. Wang, W., Lozano-Durán, A., Helmig, R., & Chu, X. (2022). Spatial and spectral characteristics of information flux between turbulent boundary layers and porous media. Journal of Fluid Mechanics, 949. https://doi.org/10.1017/jfm.2022.770
    • BibTeX
    • Link

    BibTeX

    @article{Wang2022, author = {Wang, Wenkang and Lozano-Durán, Adrián and Helmig, Rainer and Chu, Xu}, doi = {10.1017/jfm.2022.770}, issn = {1469-7645}, journal = {Journal of Fluid Mechanics}, month = {09}, publisher = {Cambridge University Press (CUP)}, title = {Spatial and spectral characteristics of information flux between turbulent boundary layers and porous media}, url = {http://dx.doi.org/10.1017/jfm.2022.770}, volume = 949, year = 2022 }

    Link

    http://dx.doi.org/10.1017/jfm.2022.770
20. Becker, B., Guo, B., Buntic, I., Flemisch, B., & Helmig, R. (2022). An Adaptive Hybrid Vertical Equilibrium/Full-Dimensional Model for Compositional Multiphase Flow. Water Resources Research, 58(1), Article 1. https://doi.org/10.1029/2021WR030990
    • Abstract
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    • Link

    Abstract

    Abstract Efficient compositional models are required to simulate underground gas storage in porous formations where, for example, gas quality (such as purity) and loss of gas due to dissolution are of interest. We first extend the concept of vertical equilibrium (VE) to compositional flow, and derive a compositional VE model by vertical integration. Second, we present a hybrid model that couples the efficient compositional VE model to a compositional full-dimensional model. Subdomains, where the compositional VE model is valid, are identified during simulation based on a VE criterion that compares the vertical profiles of relative permeability at equilibrium to the ones simulated by the full-dimensional model. We demonstrate the applicability of the hybrid model by simulating hydrogen storage in a radially symmetric, heterogeneous porous aquifer. The hybrid model shows excellent adaptivity over space and time for different permeability values in the heterogeneous region, and compares well to the full-dimensional model while being computationally efficient, resulting in a runtime of roughly one-third of the full-dimensional model. Based on the results, we assume that for larger simulation scales, the efficiency of this new model will increase even more.

    BibTeX

    @article{https://doi.org/10.1029/2021WR030990, abstract = {Abstract Efficient compositional models are required to simulate underground gas storage in porous formations where, for example, gas quality (such as purity) and loss of gas due to dissolution are of interest. We first extend the concept of vertical equilibrium (VE) to compositional flow, and derive a compositional VE model by vertical integration. Second, we present a hybrid model that couples the efficient compositional VE model to a compositional full-dimensional model. Subdomains, where the compositional VE model is valid, are identified during simulation based on a VE criterion that compares the vertical profiles of relative permeability at equilibrium to the ones simulated by the full-dimensional model. We demonstrate the applicability of the hybrid model by simulating hydrogen storage in a radially symmetric, heterogeneous porous aquifer. The hybrid model shows excellent adaptivity over space and time for different permeability values in the heterogeneous region, and compares well to the full-dimensional model while being computationally efficient, resulting in a runtime of roughly one-third of the full-dimensional model. Based on the results, we assume that for larger simulation scales, the efficiency of this new model will increase even more.}, author = {Becker, Beatrix and Guo, Bo and Buntic, Ivan and Flemisch, Bernd and Helmig, Rainer}, doi = {https://doi.org/10.1029/2021WR030990}, eprint = {https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2021WR030990}, journal = {Water Resources Research}, month = {01}, note = {e2021WR030990 2021WR030990}, number = 1, pages = {e2021WR030990}, title = {An Adaptive Hybrid Vertical Equilibrium/Full-Dimensional Model for Compositional Multiphase Flow}, url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2021WR030990}, volume = 58, year = 2022 }

    Link

    https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2021WR030990
21. Younes, A., Hoteit, H., Helmig, R., & Fahs, M. (2022). A robust fully mixed finite element model for flow and transport in unsaturated fractured porous media. Advances in Water Resources, 166, 104259. https://doi.org/10.1016/j.advwatres.2022.104259
    • Abstract
    • BibTeX
    • Link

    Abstract

    A fully mixed finite element (MFE) model is developed for nonlinear flow and transport in unsaturated fractured porous media with matrix-fracture and fracture-fracture fluid and mass exchanges. The model is based on the discrete fracture matrix (DFM) approach and assumes cross-flow equilibrium in the fractures. The MFE method is employed for the spatial discretization of both flow and transport on the 2D-matrix elements as well as on the 1D-fracture elements. An upwind scheme is employed to avoid unphysical oscillations in the case of advection dominant transport. The temporal discretization is performed using high-order time integration methods and efficient automatic time-stepping schemes via the MOL. Two test problems dealing with flow and mass transport in saturated and unsaturated fractured porous media are simulated to show the validity of the new model by comparison against (i) a 1D-2D Comsol finite element model and (ii) a 2D-2D Discontinuous Galerkin (DG) model where both fractures and matrix continua are discretized with small 2D mesh elements. The robustness and efficiency of the developed 1D-2D MFE model are then investigated for a challenging problem dealing with infiltration of contaminated water into an initially dry soil involving a fracture network. The new model yields stable results for advection-dominated and advection-dispersion transport configurations. Further, the results of the 1D-2D MFE model are in very good agreement with those of the 2D-2D DG model for both configurations. The simulation of infiltration of contaminated water into a dry fractured soil shows that the 1D-2D MFE model is within 15 times more efficient than the 2D-2D DG model, which confirms the high benefit of using robust and efficient DFM models for the simulation of flow and transport in fractured porous media.

    BibTeX

    @article{YOUNES2022104259, abstract = {A fully mixed finite element (MFE) model is developed for nonlinear flow and transport in unsaturated fractured porous media with matrix-fracture and fracture-fracture fluid and mass exchanges. The model is based on the discrete fracture matrix (DFM) approach and assumes cross-flow equilibrium in the fractures. The MFE method is employed for the spatial discretization of both flow and transport on the 2D-matrix elements as well as on the 1D-fracture elements. An upwind scheme is employed to avoid unphysical oscillations in the case of advection dominant transport. The temporal discretization is performed using high-order time integration methods and efficient automatic time-stepping schemes via the MOL. Two test problems dealing with flow and mass transport in saturated and unsaturated fractured porous media are simulated to show the validity of the new model by comparison against (i) a 1D-2D Comsol finite element model and (ii) a 2D-2D Discontinuous Galerkin (DG) model where both fractures and matrix continua are discretized with small 2D mesh elements. The robustness and efficiency of the developed 1D-2D MFE model are then investigated for a challenging problem dealing with infiltration of contaminated water into an initially dry soil involving a fracture network. The new model yields stable results for advection-dominated and advection-dispersion transport configurations. Further, the results of the 1D-2D MFE model are in very good agreement with those of the 2D-2D DG model for both configurations. The simulation of infiltration of contaminated water into a dry fractured soil shows that the 1D-2D MFE model is within 15 times more efficient than the 2D-2D DG model, which confirms the high benefit of using robust and efficient DFM models for the simulation of flow and transport in fractured porous media.}, author = {Younes, Anis and Hoteit, Hussein and Helmig, Rainer and Fahs, Marwan}, doi = {https://doi.org/10.1016/j.advwatres.2022.104259}, issn = {0309-1708}, journal = {Advances in Water Resources}, month = {08}, pages = 104259, title = {A robust fully mixed finite element model for flow and transport in unsaturated fractured porous media}, url = {https://www.sciencedirect.com/science/article/pii/S0309170822001294}, volume = 166, year = 2022 }

    Link

    https://www.sciencedirect.com/science/article/pii/S0309170822001294
22. Eller, J., Sauerborn, T., Becker, B., Buntic, I., Gross, J., & Helmig, R. (2022). Modeling Subsurface Hydrogen Storage With Transport Properties From Entropy Scaling Using the PC-SAFT Equation of State. Water Resources Research, 58(4), Article 4. https://doi.org/10.1029/2021WR030885
    • Abstract
    • BibTeX
    • Link

    Abstract

    Abstract Hydrogen is a promising alternative to carbon based energy carriers and may be stored in large quantities in subsurface storage deposits. This work assesses the impact of static (density and phase equilibria) and dynamic (viscosity and diffusion coefficients) properties on the pressure field during the injection and extraction of hydrogen in the porous subsurface. In a first step, we derive transport properties for water, hydrogen and their mixture using the Perturbed-Chain Statistical Associating Fluid Theory equation of state in combination with an entropy scaling approach and compare model predictions to alternative models from the literature. Our model compares excellently to experimental transport coefficients and models from literature with a higher number of adjustable parameters, such as GERG2008, and shows a clear improvement over empirical correlations for transport coefficients of hydrogen. In a second step, we determine the effect of further model reduction by comparing our against a much simpler model applying empirical transport coefficients from the literature. For this purpose, hydrogen is periodically injected into and extracted out of a dome-shaped porous aquifer under a caprock. Our results show that density and viscosity of hydrogen have the highest impact on the pressure field, and that a thermodynamic model like the new model presented here is essential for modeling the storage aquifer, while keeping the number of coefficients at a minimum. In diffusion-dominated settings such as the diffusion of hydrogen through the caprock, our developed diffusion coefficients show a much improved dependence on temperature and pressure, leading to a more accurate approximation of the diffusive fluxes.

    BibTeX

    @article{https://doi.org/10.1029/2021WR030885, abstract = {Abstract Hydrogen is a promising alternative to carbon based energy carriers and may be stored in large quantities in subsurface storage deposits. This work assesses the impact of static (density and phase equilibria) and dynamic (viscosity and diffusion coefficients) properties on the pressure field during the injection and extraction of hydrogen in the porous subsurface. In a first step, we derive transport properties for water, hydrogen and their mixture using the Perturbed-Chain Statistical Associating Fluid Theory equation of state in combination with an entropy scaling approach and compare model predictions to alternative models from the literature. Our model compares excellently to experimental transport coefficients and models from literature with a higher number of adjustable parameters, such as GERG2008, and shows a clear improvement over empirical correlations for transport coefficients of hydrogen. In a second step, we determine the effect of further model reduction by comparing our against a much simpler model applying empirical transport coefficients from the literature. For this purpose, hydrogen is periodically injected into and extracted out of a dome-shaped porous aquifer under a caprock. Our results show that density and viscosity of hydrogen have the highest impact on the pressure field, and that a thermodynamic model like the new model presented here is essential for modeling the storage aquifer, while keeping the number of coefficients at a minimum. In diffusion-dominated settings such as the diffusion of hydrogen through the caprock, our developed diffusion coefficients show a much improved dependence on temperature and pressure, leading to a more accurate approximation of the diffusive fluxes.}, author = {Eller, Johannes and Sauerborn, Tim and Becker, Beatrix and Buntic, Ivan and Gross, Joachim and Helmig, Rainer}, doi = {https://doi.org/10.1029/2021WR030885}, eprint = {https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2021WR030885}, journal = {Water Resources Research}, month = {04}, note = {e2021WR030885 2021WR030885}, number = 4, pages = {e2021WR030885}, title = {Modeling Subsurface Hydrogen Storage With Transport Properties From Entropy Scaling Using the PC-SAFT Equation of State}, url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2021WR030885}, volume = 58, year = 2022 }

    Link

    https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2021WR030885
23. Weishaupt, K., Koch, T., & Helmig, R. (2022). A fully implicit coupled pore-network/free-flow model for the pore-scale simulation of drying processes. Drying Technology, 40(4), Article 4. https://doi.org/10.1080/07373937.2021.1955706
    • Abstract
    • BibTeX
    • Link

    Abstract

    We present a fully coupled pore-network/free-flow model providing pore-scale insight into drying processes. We solve the Navier–Stokes equations with component transport in the free-flow region, coupled to a dynamic two-phase, two-component pore-network model (PNM) in the porous domain. The dynamic multi-physics model allows to temporally resolve drying processes in-between capillary equilibrium states. All simulations are non-isothermal and use pressure- and temperature-depended fluid properties. Carefully chosen coupling conditions and a monolithic solver ensure local conservation of mass, momentum, and energy fluxes, in particular at the interface between both model domains. We solve for wetting and non-wetting fluid pressure fields and consider advective gas transport in the network. Numerical examples demonstrate that the coupled model is able to cover a wide range of physical processes relevant for drying and show the mutual interaction of the two subregions. The model is implemented in the modular open-source framework DuMux such that extensions are straight-forward.

    BibTeX

    @article{doi:10.1080/07373937.2021.1955706, abstract = { We present a fully coupled pore-network/free-flow model providing pore-scale insight into drying processes. We solve the Navier–Stokes equations with component transport in the free-flow region, coupled to a dynamic two-phase, two-component pore-network model (PNM) in the porous domain. The dynamic multi-physics model allows to temporally resolve drying processes in-between capillary equilibrium states. All simulations are non-isothermal and use pressure- and temperature-depended fluid properties. Carefully chosen coupling conditions and a monolithic solver ensure local conservation of mass, momentum, and energy fluxes, in particular at the interface between both model domains. We solve for wetting and non-wetting fluid pressure fields and consider advective gas transport in the network. Numerical examples demonstrate that the coupled model is able to cover a wide range of physical processes relevant for drying and show the mutual interaction of the two subregions. The model is implemented in the modular open-source framework DuMux such that extensions are straight-forward. }, author = {Weishaupt, Kilian and Koch, Timo and Helmig, Rainer}, doi = {10.1080/07373937.2021.1955706}, eprint = {https://doi.org/10.1080/07373937.2021.1955706}, journal = {Drying Technology}, month = {08}, number = 4, pages = {697-718}, publisher = {Taylor & Francis}, title = {A fully implicit coupled pore-network/free-flow model for the pore-scale simulation of drying processes}, url = {/brokenurl# https://doi.org/10.1080/07373937.2021.1955706 }, volume = 40, year = 2022 }

    Link

    /brokenurl# https://doi.org/10.1080/07373937.2021.1955706
24. Michalkowski, C., Veyskarami, M., Bringedal, C., Helmig, R., & Schleper, V. (2022). Two-phase Flow Dynamics at the Interface Between GDL and Gas Distributor Channel Using a Pore-Network Model. Transport in Porous Media, 144(2), Article 2. https://doi.org/10.1007/s11242-022-01813-4
    • Abstract
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    • Link

    Abstract

    For improved operating conditions of a polymer electrolyte membrane (PEM) fuel cell, a sophisticated water management is crucial. Therefore, it is necessary to understand the transport mechanisms of water throughout the cell constituents especially on the cathode side, where the excess water has to be removed. Pore-scale modeling of diffusion layers and gas distributor has been established as a favorable technique to investigate the ongoing processes. Investigating the interface between the cathode layers, a particular challenge is the combination and interaction of the multi-phase flow in the porous material of the gas diffusion layer (GDL) with the free flow in the gas distributor channels. The formation, growth and detachment of water droplets on the hydrophobic, porous surface of the GDL have a major influence on the mass, momentum and energy exchange between the layers. A dynamic pore-network model is used to describe the flow through the porous GDL on the pore-scale. To capture the droplet occurrence and its influence on the flow, this dynamic two-phase pore-network model is extended to capture droplet formation and growth at the surface of the GDL as well as droplet detachment due to the gas flow in the gas distributor channels. In this article, the developed model is applied to single- and multi-tube systems to investigate the general drop behavior. These rather simple test-cases are compared to experimental and numerical data available in the literature. Finally, the model is applied to a GDL unit cell to analyze the interaction between two-phase flow through the GDL and drop formation at the interface between GDL and gas distributor channel.

    BibTeX

    @article{michalkowski_two-phase_2022, abstract = {For improved operating conditions of a polymer electrolyte membrane (PEM) fuel cell, a sophisticated water management is crucial. Therefore, it is necessary to understand the transport mechanisms of water throughout the cell constituents especially on the cathode side, where the excess water has to be removed. Pore-scale modeling of diffusion layers and gas distributor has been established as a favorable technique to investigate the ongoing processes. Investigating the interface between the cathode layers, a particular challenge is the combination and interaction of the multi-phase flow in the porous material of the gas diffusion layer (GDL) with the free flow in the gas distributor channels. The formation, growth and detachment of water droplets on the hydrophobic, porous surface of the GDL have a major influence on the mass, momentum and energy exchange between the layers. A dynamic pore-network model is used to describe the flow through the porous GDL on the pore-scale. To capture the droplet occurrence and its influence on the flow, this dynamic two-phase pore-network model is extended to capture droplet formation and growth at the surface of the GDL as well as droplet detachment due to the gas flow in the gas distributor channels. In this article, the developed model is applied to single- and multi-tube systems to investigate the general drop behavior. These rather simple test-cases are compared to experimental and numerical data available in the literature. Finally, the model is applied to a GDL unit cell to analyze the interaction between two-phase flow through the GDL and drop formation at the interface between GDL and gas distributor channel.}, author = {Michalkowski, Cynthia and Veyskarami, Maziar and Bringedal, Carina and Helmig, Rainer and Schleper, Veronika}, doi = {10.1007/s11242-022-01813-4}, issn = {1573-1634}, journal = {Transport in Porous Media}, month = {09}, number = 2, pages = {429--458}, title = {Two-phase Flow Dynamics at the Interface Between GDL and Gas Distributor Channel Using a Pore-Network Model}, url = {https://doi.org/10.1007/s11242-022-01813-4}, volume = 144, year = 2022 }

    Link

    https://doi.org/10.1007/s11242-022-01813-4
25. Kurgyis, K., Hommel, J., Flemisch, B., Helmig, R., & Ott, H. (2021). Explicit continuum scale modeling of low-salinity mechanisms. Journal of Petroleum Science and Engineering, 199, 108336. https://doi.org/10.1016/j.petrol.2020.108336
    • Abstract
    • BibTeX
    • Link

    Abstract

    Understanding the influence of injection water composition on the displacement efficiency has been a long-standing issue in reservoir engineering; a reduction of the injection water salinity can lead to additional oil production, which is considered a low-cost and environmentally friendly method for enhanced oil recovery. Several underlying chemical mechanisms have been identified; however, the identification of the governing mechanisms remains difficult and specific to the chemical setting of the reservoir and injection water composition. In this work, we implement two potential mechanisms, namely, double layer expansion and multicomponent ion exchange, to achieve an explicit description of low-salinity effects in the open-source continuum-scale flow simulator DuMuX, with the goal of designing and interpreting experiments, and upscaling the results. By assuming sets of input parameters, we show that there is a minimum required core length dependent on the dispersion of the chemical flooding front dominated by sample heterogeneity. Above this length scale, the saturation profile is fully developed, and the chemical effluent analysis is conclusive, which both is required to calibrate continuum scale models. The change in the chemical water composition shows a characteristic fingerprint for both investigated mechanisms and therefore allows the identification of the leading low-salinity mechanism. The model is publicly available.

    BibTeX

    @article{KURGYIS2021108336, abstract = {Understanding the influence of injection water composition on the displacement efficiency has been a long-standing issue in reservoir engineering; a reduction of the injection water salinity can lead to additional oil production, which is considered a low-cost and environmentally friendly method for enhanced oil recovery. Several underlying chemical mechanisms have been identified; however, the identification of the governing mechanisms remains difficult and specific to the chemical setting of the reservoir and injection water composition. In this work, we implement two potential mechanisms, namely, double layer expansion and multicomponent ion exchange, to achieve an explicit description of low-salinity effects in the open-source continuum-scale flow simulator DuMuX, with the goal of designing and interpreting experiments, and upscaling the results. By assuming sets of input parameters, we show that there is a minimum required core length dependent on the dispersion of the chemical flooding front dominated by sample heterogeneity. Above this length scale, the saturation profile is fully developed, and the chemical effluent analysis is conclusive, which both is required to calibrate continuum scale models. The change in the chemical water composition shows a characteristic fingerprint for both investigated mechanisms and therefore allows the identification of the leading low-salinity mechanism. The model is publicly available.}, author = {Kurgyis, Kata and Hommel, Johannes and Flemisch, Bernd and Helmig, Rainer and Ott, Holger}, doi = {10.1016/j.petrol.2020.108336}, issn = {0920-4105}, journal = {Journal of Petroleum Science and Engineering}, month = {04}, pages = 108336, publisher = {Elsevier {BV}}, title = {Explicit continuum scale modeling of low-salinity mechanisms}, url = {http://www.sciencedirect.com/science/article/pii/S0920410520313905}, volume = 199, year = 2021 }

    Link

    http://www.sciencedirect.com/science/article/pii/S0920410520313905
26. Weishaupt, K., Koch, T., & Helmig, R. (2021). A fully implicit coupled pore-network/free-flow model for the pore-scale simulation of drying processes. Drying Technology, 0(0), Article 0. https://doi.org/10.1080/07373937.2021.1955706
    • Abstract
    • BibTeX
    • Link

    Abstract

    We present a fully coupled pore-network/free-flow model providing pore-scale insight into drying processes. We solve the Navier–Stokes equations with component transport in the free-flow region, coupled to a dynamic two-phase, two-component pore-network model (PNM) in the porous domain. The dynamic multi-physics model allows to temporally resolve drying processes in-between capillary equilibrium states. All simulations are non-isothermal and use pressure- and temperature-depended fluid properties. Carefully chosen coupling conditions and a monolithic solver ensure local conservation of mass, momentum, and energy fluxes, in particular at the interface between both model domains. We solve for wetting and non-wetting fluid pressure fields and consider advective gas transport in the network. Numerical examples demonstrate that the coupled model is able to cover a wide range of physical processes relevant for drying and show the mutual interaction of the two subregions. The model is implemented in the modular open-source framework DuMux such that extensions are straight-forward.

    BibTeX

    @article{weishaupt2021, abstract = { We present a fully coupled pore-network/free-flow model providing pore-scale insight into drying processes. We solve the Navier–Stokes equations with component transport in the free-flow region, coupled to a dynamic two-phase, two-component pore-network model (PNM) in the porous domain. The dynamic multi-physics model allows to temporally resolve drying processes in-between capillary equilibrium states. All simulations are non-isothermal and use pressure- and temperature-depended fluid properties. Carefully chosen coupling conditions and a monolithic solver ensure local conservation of mass, momentum, and energy fluxes, in particular at the interface between both model domains. We solve for wetting and non-wetting fluid pressure fields and consider advective gas transport in the network. Numerical examples demonstrate that the coupled model is able to cover a wide range of physical processes relevant for drying and show the mutual interaction of the two subregions. The model is implemented in the modular open-source framework DuMux such that extensions are straight-forward. }, author = {Weishaupt, Kilian and Koch, Timo and Helmig, Rainer}, doi = {10.1080/07373937.2021.1955706}, eprint = {https://doi.org/10.1080/07373937.2021.1955706}, journal = {Drying Technology}, month = {04}, number = 0, pages = {1--22}, publisher = {Informa {UK} Limited}, title = {A fully implicit coupled pore-network/free-flow model for the pore-scale simulation of drying processes}, url = {https://doi.org/10.1080/07373937.2021.1955706}, volume = 0, year = 2021 }

    Link

    https://doi.org/10.1080/07373937.2021.1955706
27. Wang, W. (王文康), Yang, G. (杨光), Evrim, C., Terzis, A., Helmig, R., & Chu, X. (初旭). (2021). An assessment of turbulence transportation near regular and random permeable interfaces. Physics of Fluids, 33(11), Article 11. https://doi.org/10.1063/5.0069311
    • BibTeX
    • Link

    BibTeX

    @article{wang_assessment_2021, annote = {doi: 10.1063/5.0069311}, author = {Wang, Wenkang (王文康) and Yang, Guang (杨光) and Evrim, Cenk and Terzis, Alexandros and Helmig, Rainer and Chu, Xu (初旭)}, doi = {10.1063/5.0069311}, issn = {1070-6631}, journal = {Physics of Fluids}, month = {11}, note = {Publisher: American Institute of Physics}, number = 11, pages = 115103, title = {An assessment of turbulence transportation near regular and random permeable interfaces}, url = {https://doi.org/10.1063/5.0069311}, urldate = {2022-11-16}, volume = 33, year = 2021 }

    Link

    https://doi.org/10.1063/5.0069311
28. Schneider, J., Groh, J., Pütz, T., Helmig, R., Rothfuss, Y., Vereecken, H., & Vanderborght, J. (2021). Prediction of soil evaporation measured with weighable lysimeters using the FAO Penman–Monteith method in combination with Richards’ equation. Vadose Zone Journal, 20(1), Article 1. https://doi.org/10.1002/vzj2.20102
    • Abstract
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    • Link

    Abstract

    Abstract Multiannual data (2016–2018) from 12 weighed lysimeters (four soil types with textures ranging from sandy loam to silt loam, three replicates) of the TERENO SOILCan network were used to evaluate if evaporation (E) rates could be predicted from weather data using the FAO Penman–Monteith (PM) method combined with soil water flow simulations using the Richards equation. Soil hydraulic properties (SHPs) were estimated either from soil texture using the ROSETTA pedotransfer functions, from in situ measured water retention curves, or from soil surface water contents using inverse modeling. In all years, E was water limited and the measured evaporation rates (Em) surprisingly did not vary significantly among the four different soil types. When SHPs derived from pedotransfer functions were used, simulated evaporation rates of the finer textured soils overestimated the measured ones considerably. Better agreement was obtained when simulations were based on in situ measured or inversely estimated SHPs. The SHPs estimated from pedotransfer functions represented unrealistically large characteristic lengths of evaporation (Lc), and Lc was found to be a useful characteristic to constrain estimates of SHPs. Also, when soil evaporation was water limited and Em rates were below Epot (PM evaporation scaled by an empirical coefficient), the diurnal dynamics of Em followed those of Epot. The Richards equation that considers only isothermal liquid water flow did not reproduce these dynamics caused by temperature dependent vapor transport in the soil.

    BibTeX

    @article{schneider_prediction_2021, abstract = {Abstract Multiannual data (2016–2018) from 12 weighed lysimeters (four soil types with textures ranging from sandy loam to silt loam, three replicates) of the TERENO SOILCan network were used to evaluate if evaporation (E) rates could be predicted from weather data using the FAO Penman–Monteith (PM) method combined with soil water flow simulations using the Richards equation. Soil hydraulic properties (SHPs) were estimated either from soil texture using the ROSETTA pedotransfer functions, from in situ measured water retention curves, or from soil surface water contents using inverse modeling. In all years, E was water limited and the measured evaporation rates (Em) surprisingly did not vary significantly among the four different soil types. When SHPs derived from pedotransfer functions were used, simulated evaporation rates of the finer textured soils overestimated the measured ones considerably. Better agreement was obtained when simulations were based on in situ measured or inversely estimated SHPs. The SHPs estimated from pedotransfer functions represented unrealistically large characteristic lengths of evaporation (Lc), and Lc was found to be a useful characteristic to constrain estimates of SHPs. Also, when soil evaporation was water limited and Em rates were below Epot (PM evaporation scaled by an empirical coefficient), the diurnal dynamics of Em followed those of Epot. The Richards equation that considers only isothermal liquid water flow did not reproduce these dynamics caused by temperature dependent vapor transport in the soil.}, author = {Schneider, Jana and Groh, Jannis and Pütz, Thomas and Helmig, Rainer and Rothfuss, Youri and Vereecken, Harry and Vanderborght, Jan}, doi = {https://doi.org/10.1002/vzj2.20102}, journal = {Vadose Zone Journal}, number = 1, pages = {e20102}, title = {Prediction of soil evaporation measured with weighable lysimeters using the FAO Penman–Monteith method in combination with Richards’ equation}, url = {https://acsess.onlinelibrary.wiley.com/doi/abs/10.1002/vzj2.20102}, volume = 20, year = 2021 }

    Link

    https://acsess.onlinelibrary.wiley.com/doi/abs/10.1002/vzj2.20102
29. Ackermann, S., Bringedal, C., & Helmig, R. (2021). Multi-scale three-domain approach for coupling free flow and flow in porous media including droplet-related interface processes. Journal of Computational Physics, 429, 109993. https://doi.org/10.1016/j.jcp.2020.109993
    • Abstract
    • BibTeX
    • Link

    Abstract

    Drops on a free-flow/porous-medium-flow interface have a strong influence on the exchange of mass, momentum and energy between the two macroscopic flow regimes. Modeling droplet-related pore-scale processes in a macro-scale context is challenging due to the scale gap, but might be rewarding due to relatively low computational costs. We develop a three-domain approach to model drop formation, growth, detachment and film flow in a lower-dimensional interface domain. A simple upscaling technique allows to compute the drop-covered interface area fraction which affects the coupling fluxes. In a first scenario, only drop formation, growth and detachment are taken into account. Then, spreading and merging due to lateral fluxes are considered as well. The simulation results show that the impact of these droplet-related processes can be captured. However, extensions are necessary to represent the influence on the free flow more precisely.

    BibTeX

    @article{ackermann-bringedal-helmig-2021, abstract = {Drops on a free-flow/porous-medium-flow interface have a strong influence on the exchange of mass, momentum and energy between the two macroscopic flow regimes. Modeling droplet-related pore-scale processes in a macro-scale context is challenging due to the scale gap, but might be rewarding due to relatively low computational costs. We develop a three-domain approach to model drop formation, growth, detachment and film flow in a lower-dimensional interface domain. A simple upscaling technique allows to compute the drop-covered interface area fraction which affects the coupling fluxes. In a first scenario, only drop formation, growth and detachment are taken into account. Then, spreading and merging due to lateral fluxes are considered as well. The simulation results show that the impact of these droplet-related processes can be captured. However, extensions are necessary to represent the influence on the free flow more precisely.}, author = {Ackermann, Sina and Bringedal, Carina and Helmig, Rainer}, doi = {https://doi.org/10.1016/j.jcp.2020.109993}, issn = {0021-9991}, journal = {Journal of Computational Physics}, month = {03}, pages = 109993, publisher = {Elsevier BV}, title = {Multi-scale three-domain approach for coupling free flow and flow in porous media including droplet-related interface processes}, url = {http://www.sciencedirect.com/science/article/pii/S0021999120307671}, volume = 429, year = 2021 }

    Link

    http://www.sciencedirect.com/science/article/pii/S0021999120307671
30. Chu, X., Wang, W., Yang, G., Terzis, A., Helmig, R., & Weigand, B. (2021). Transport of Turbulence Across Permeable Interface in a Turbulent Channel Flow: Interface-Resolved Direct Numerical Simulation. Transport in Porous Media, 136(1), Article 1. https://doi.org/10.1007/s11242-020-01506-w
    • Abstract
    • BibTeX
    • Link

    Abstract

    Turbulence transportation across permeable interfaces is investigated using direct numerical simulation, and the connection between the turbulent surface flow and the pore flow is explored. The porous media domain is constructed with an in-line arranged circular cylinder array. The effects of Reynolds number and porosity are also investigated by comparing cases with two Reynolds numbers (\$\$Re\textbackslashapprox 3000,6000\$\$) and two porosities (\$\$\textbackslashvarphi =0.5,0.8\$\$). It was found that the change of porosity leads to the variation of flow motions near the interface region, which further affect turbulence transportation below the interface. The turbulent kinetic energy (TKE) budget shows that turbulent diffusion and pressure transportation work as energy sink and source alternatively, which suggests a possible route for turbulence transferring into porous region. Further analysis on the spectral TKE budget reveals the role of modes of different wavelengths. A major finding is that mean convection not only affects the distribution of TKE in spatial space, but also in scale space. The permeability of the wall also have an major impact on the occurrence ratio between blow and suction events as well as their corresponding flow structures, which can be related to the change of the Kármán constant of the mean velocity profile.

    BibTeX

    @article{chu_transport_2021, abstract = {Turbulence transportation across permeable interfaces is investigated using direct numerical simulation, and the connection between the turbulent surface flow and the pore flow is explored. The porous media domain is constructed with an in-line arranged circular cylinder array. The effects of Reynolds number and porosity are also investigated by comparing cases with two Reynolds numbers (\$\$Re{\textbackslash}approx 3000,6000\$\$) and two porosities (\$\${\textbackslash}varphi =0.5,0.8\$\$). It was found that the change of porosity leads to the variation of flow motions near the interface region, which further affect turbulence transportation below the interface. The turbulent kinetic energy (TKE) budget shows that turbulent diffusion and pressure transportation work as energy sink and source alternatively, which suggests a possible route for turbulence transferring into porous region. Further analysis on the spectral TKE budget reveals the role of modes of different wavelengths. A major finding is that mean convection not only affects the distribution of TKE in spatial space, but also in scale space. The permeability of the wall also have an major impact on the occurrence ratio between blow and suction events as well as their corresponding flow structures, which can be related to the change of the Kármán constant of the mean velocity profile.}, author = {Chu, Xu and Wang, Wenkang and Yang, Guang and Terzis, Alexandros and Helmig, Rainer and Weigand, Bernhard}, doi = {10.1007/s11242-020-01506-w}, issn = {1573-1634}, journal = {Transport in Porous Media}, month = {01}, number = 1, pages = {165--189}, title = {Transport of Turbulence Across Permeable Interface in a Turbulent Channel Flow: Interface-Resolved Direct Numerical Simulation}, url = {https://doi.org/10.1007/s11242-020-01506-w}, volume = 136, year = 2021 }

    Link

    https://doi.org/10.1007/s11242-020-01506-w
31. Gao, B., Coltman, E., Farnsworth, J., Helmig, R., & Smits, K. M. (2021). Determination of Vapor and Momentum Roughness Lengths Above an Undulating Soil Surface Based on PIV-Measured Velocity Profiles. Water Resources Research, 57(7), Article 7. https://doi.org/10.1029/2021WR029578
    • Abstract
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    Abstract

    Abstract Accurately predicting bare-soil evaporation requires the proper characterization of the near-surface atmospheric conditions. These conditions, dependent on factors such as surface microtopography and wind velocity, vary greatly and therefore require high-resolution datasets to be fully incorporated into evaporation models. These factors are oftentimes parameterized in models through the aerodynamic resistance (ra), in which the vapor roughness length (z0v) and the momentum roughness length (z0m) are two crucial parameters that describe the transport near the soil-atmosphere interface. Typically, when evaluating bare-soil evaporation, these two characteristic lengths are assumed equal, although differences are likely to occur especially in turbulent flows over undulating surfaces. Thus, this study aims to investigate the relationship between z0v and z0m above undulating surfaces to ultimately improve accuracy in estimating evaporation rate. To achieve this goal, four uniquely designed wind tunnel—soil tank experiments were conducted considering different wind speeds and undulation spacings. Particle image velocimetry (PIV) was used to measure the velocity field above the undulating surface in high resolution. Using the high-fidelity data set, the logarithmic ratio of z0v to z0m is determined and used to estimate ra. Results confirm that these lengths differ significantly, with the logarithmic ratio roughly ranging from −15 to −5 under the conditions tested. PIV-measured results demonstrate this ratio is closely tied to the mass and momentum transport behaviors influenced by surface undulations. Using the data-integrated formulation of ra, predictions of evaporation rate were prepared for both the laboratory and lysimeter experiments, demonstrating the efficacy of the proposed approach in this study.

    BibTeX

    @article{gao2021a, abstract = {Abstract Accurately predicting bare-soil evaporation requires the proper characterization of the near-surface atmospheric conditions. These conditions, dependent on factors such as surface microtopography and wind velocity, vary greatly and therefore require high-resolution datasets to be fully incorporated into evaporation models. These factors are oftentimes parameterized in models through the aerodynamic resistance (ra), in which the vapor roughness length (z0v) and the momentum roughness length (z0m) are two crucial parameters that describe the transport near the soil-atmosphere interface. Typically, when evaluating bare-soil evaporation, these two characteristic lengths are assumed equal, although differences are likely to occur especially in turbulent flows over undulating surfaces. Thus, this study aims to investigate the relationship between z0v and z0m above undulating surfaces to ultimately improve accuracy in estimating evaporation rate. To achieve this goal, four uniquely designed wind tunnel—soil tank experiments were conducted considering different wind speeds and undulation spacings. Particle image velocimetry (PIV) was used to measure the velocity field above the undulating surface in high resolution. Using the high-fidelity data set, the logarithmic ratio of z0v to z0m is determined and used to estimate ra. Results confirm that these lengths differ significantly, with the logarithmic ratio roughly ranging from −15 to −5 under the conditions tested. PIV-measured results demonstrate this ratio is closely tied to the mass and momentum transport behaviors influenced by surface undulations. Using the data-integrated formulation of ra, predictions of evaporation rate were prepared for both the laboratory and lysimeter experiments, demonstrating the efficacy of the proposed approach in this study.}, author = {Gao, Bo and Coltman, Edward and Farnsworth, John and Helmig, Rainer and Smits, Kathleen M.}, doi = {10.1029/2021WR029578}, eprint = {https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2021WR029578}, journal = {Water Resources Research}, month = {06}, number = 7, pages = {e2021WR029578}, title = {Determination of Vapor and Momentum Roughness Lengths Above an Undulating Soil Surface Based on PIV-Measured Velocity Profiles}, url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2021WR029578}, volume = 57, year = 2021 }

    Link

    https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2021WR029578
32. Wang, W., Chu, X., Lozano-Durán, A., Helmig, R., & Weigand, B. (2021). Information transfer between turbulent boundary layers and porous media. Journal of Fluid Mechanics, 920, A21. https://doi.org/10.1017/jfm.2021.445
    • Abstract
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    Abstract

    The interaction between the flow above and below a permeable wall is a central topic in the study of porous media. While previous investigations have provided compelling evidence of the strong coupling between the two regions, few studies have quantitatively measured the directionality, i.e. cause-and-effect relations, of this interaction. To shed light on the problem, interface-resolved direct numerical simulations of channel flow over a cylinder array for porosity \$\textbackslashvarphi =0.4\$–\$0.9\$ are performed, and the friction Reynolds number of the top smooth wall is controlled to be \$Re\_\\textbackslashtau \\textbackslashapprox 180\$. We use transfer entropy as a marker to evaluate the causal interaction between the free turbulent flow and the porous medium. Correlation analysis and linear coherence spectra are also leveraged to complete the study. Our results show that the permeability of the porous medium has a profound impact on the intensity, time scale and spatial extent of surface–subsurface interactions. The interaction of the free flow and porous medium is further decomposed into two coupling directions, namely, top-down and bottom-up. For low-porosity cases, top-down and bottom-up interactions are strongly asymmetric, the former being mostly influenced by small near-wall eddies, and the latter reflecting the onset of Kelvin–Helmholtz type instabilities due to the perturbation from the porous medium. As the porosity increases, both top-down and bottom-up interactions are dominated by shear-flow instabilities.

    BibTeX

    @article{wang_information_2021, abstract = {The interaction between the flow above and below a permeable wall is a central topic in the study of porous media. While previous investigations have provided compelling evidence of the strong coupling between the two regions, few studies have quantitatively measured the directionality, i.e. cause-and-effect relations, of this interaction. To shed light on the problem, interface-resolved direct numerical simulations of channel flow over a cylinder array for porosity \${\textbackslash}varphi =0.4\$–\$0.9\$ are performed, and the friction Reynolds number of the top smooth wall is controlled to be \$Re\_\{{\textbackslash}tau \}{\textbackslash}approx 180\$. We use transfer entropy as a marker to evaluate the causal interaction between the free turbulent flow and the porous medium. Correlation analysis and linear coherence spectra are also leveraged to complete the study. Our results show that the permeability of the porous medium has a profound impact on the intensity, time scale and spatial extent of surface–subsurface interactions. The interaction of the free flow and porous medium is further decomposed into two coupling directions, namely, top-down and bottom-up. For low-porosity cases, top-down and bottom-up interactions are strongly asymmetric, the former being mostly influenced by small near-wall eddies, and the latter reflecting the onset of Kelvin–Helmholtz type instabilities due to the perturbation from the porous medium. As the porosity increases, both top-down and bottom-up interactions are dominated by shear-flow instabilities.}, author = {Wang, Wenkang and Chu, Xu and Lozano-Durán, Adrián and Helmig, Rainer and Weigand, Bernhard}, doi = {10.1017/jfm.2021.445}, issn = {0022-1120}, journal = {Journal of Fluid Mechanics}, note = {Edition: 2021/06/10Publisher: Cambridge University Press}, pages = {A21}, title = {Information transfer between turbulent boundary layers and porous media}, url = {https://www.cambridge.org/core/article/information-transfer-between-turbulent-boundary-layers-and-porous-media/6791BFCED29848AD37FA3B4D4AA5B684}, volume = 920, year = 2021 }

    Link

    https://www.cambridge.org/core/article/information-transfer-between-turbulent-boundary-layers-and-porous-media/6791BFCED29848AD37FA3B4D4AA5B684
33. Koch, T., Weishaupt, K., Müller, J., Weigand, B., & Helmig, R. (2021). A (Dual) Network Model for Heat Transfer in Porous Media. Transport in Porous Media, 140(1), Article 1. https://doi.org/10.1007/s11242-021-01602-5
    • Abstract
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    Abstract

    We present a dual network model to simulate coupled single-phase flow and energy transport in porous media including conditions under which local thermal equilibrium cannot be assumed. The models target applications such as the simulation of catalytic reactors, micro-fluidic experiments, or micro-cooling devices. The new technique is based on a recently developed algorithm that extracts both the pore space and the solid grain matrix of a porous medium from CT images into an interconnected network representation. We simulate coupled heat and mass transfer in these networks simultaneously, allowing naturally to model scenarios with heterogeneous temperature distributions in both void space and solid matrix. The model is compared with 3D conjugate heat transfer simulations for both conduction- and convection-dominated scenarios. It is shown to reproduce effective thermal conductivities over a wide range of fluid to solid thermal conductivity ratios with a single parameter set. Morevoer, it captures local thermal nonequilibrium effects in a micro-cooling device scenario.

    BibTeX

    @article{koch_dual_2021, abstract = {We present a dual network model to simulate coupled single-phase flow and energy transport in porous media including conditions under which local thermal equilibrium cannot be assumed. The models target applications such as the simulation of catalytic reactors, micro-fluidic experiments, or micro-cooling devices. The new technique is based on a recently developed algorithm that extracts both the pore space and the solid grain matrix of a porous medium from CT images into an interconnected network representation. We simulate coupled heat and mass transfer in these networks simultaneously, allowing naturally to model scenarios with heterogeneous temperature distributions in both void space and solid matrix. The model is compared with 3D conjugate heat transfer simulations for both conduction- and convection-dominated scenarios. It is shown to reproduce effective thermal conductivities over a wide range of fluid to solid thermal conductivity ratios with a single parameter set. Morevoer, it captures local thermal nonequilibrium effects in a micro-cooling device scenario.}, author = {Koch, Timo and Weishaupt, Kilian and Müller, Johannes and Weigand, Bernhard and Helmig, Rainer}, doi = {10.1007/s11242-021-01602-5}, issn = {1573-1634}, journal = {Transport in Porous Media}, month = {10}, number = 1, pages = {107--141}, title = {A (Dual) Network Model for Heat Transfer in Porous Media}, url = {https://doi.org/10.1007/s11242-021-01602-5}, volume = 140, year = 2021 }

    Link

    https://doi.org/10.1007/s11242-021-01602-5
34. Ahmadi, N., Heck, K., Rolle, M., Helmig, R., & Mosthaf, K. (2021). On multicomponent gas diffusion and coupling concepts for porous media and free flow: a benchmark study. Computational Geosciences, 25(5), Article 5. https://doi.org/10.1007/s10596-021-10057-y
    • Abstract
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    • Link

    Abstract

    Multicomponent gas transport in porous media and at the interface between porous media and free flow occurs in a wide range of technical and environmental systems. Modeling tools are required for the quantitative description of such coupled environmental compartments. We present a benchmark study to compare different diffusion models as well as different coupling concepts employed for the description of multicomponent gas flow and transport at the porous medium/free-flow interface. The benchmark problems allowed us to compare two diffusion models (Fickian and Maxwell-Stefan formulations) for predicting the transport behavior of multicomponent mixtures in porous media and in presence of a free flow. The examples highlighted the importance of interaction between different diffusing components by applying the Maxwell-Stefan formulation, as well as the impact of the free flow velocity on gas migration at the interface under diffusion- and advection-dominated conditions. The problems were solved using two simulation tools, incorporating different coupling concepts to describe the physics of flow and transport processes. In COMSOL Multiphysics, we implemented a single-domain Brinkman approach, whereas in the DuMuX simulator we used a two-domain approach with the Navier-Stokes equation for the free flow and Darcy’s law for the porous medium. Also, the formulation of the Maxwell-Stefan equation for multicomponent transport was different between the two codes. Despite the different modeling concepts, mathematical descriptions and numerical schemes implemented in the two simulators, their outcomes demonstrate excellent agreement for all benchmark problems, as well as the capability to reproduce the results of previous modeling and experimental studies.

    BibTeX

    @article{ahmadi_multicomponent_2021, abstract = {Multicomponent gas transport in porous media and at the interface between porous media and free flow occurs in a wide range of technical and environmental systems. Modeling tools are required for the quantitative description of such coupled environmental compartments. We present a benchmark study to compare different diffusion models as well as different coupling concepts employed for the description of multicomponent gas flow and transport at the porous medium/free-flow interface. The benchmark problems allowed us to compare two diffusion models (Fickian and Maxwell-Stefan formulations) for predicting the transport behavior of multicomponent mixtures in porous media and in presence of a free flow. The examples highlighted the importance of interaction between different diffusing components by applying the Maxwell-Stefan formulation, as well as the impact of the free flow velocity on gas migration at the interface under diffusion- and advection-dominated conditions. The problems were solved using two simulation tools, incorporating different coupling concepts to describe the physics of flow and transport processes. In COMSOL Multiphysics, we implemented a single-domain Brinkman approach, whereas in the DuMuX simulator we used a two-domain approach with the Navier-Stokes equation for the free flow and Darcy’s law for the porous medium. Also, the formulation of the Maxwell-Stefan equation for multicomponent transport was different between the two codes. Despite the different modeling concepts, mathematical descriptions and numerical schemes implemented in the two simulators, their outcomes demonstrate excellent agreement for all benchmark problems, as well as the capability to reproduce the results of previous modeling and experimental studies.}, author = {Ahmadi, Navid and Heck, Katharina and Rolle, Massimo and Helmig, Rainer and Mosthaf, Klaus}, doi = {10.1007/s10596-021-10057-y}, issn = {1573-1499}, journal = {Computational Geosciences}, month = {10}, number = 5, pages = {1493--1507}, title = {On multicomponent gas diffusion and coupling concepts for porous media and free flow: a benchmark study}, url = {https://doi.org/10.1007/s10596-021-10057-y}, volume = 25, year = 2021 }

    Link

    https://doi.org/10.1007/s10596-021-10057-y
35. Schneider, M., Weishaupt, K., Gläser, D., Boon, W. M., & Helmig, R. (2020). Coupling staggered-grid and MPFA finite volume methods for free flow/porous-medium flow problems. Journal of Computational Physics, 401. https://doi.org/10.1016/j.jcp.2019.109012
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    BibTeX

    @article{schneider.etAl2019, author = {Schneider, M. and Weishaupt, K. and Gläser, D. and Boon, W. M. and Helmig, R.}, doi = {https://doi.org/10.1016/j.jcp.2019.109012}, issn = {0021-9991}, journal = {Journal of Computational Physics}, title = {Coupling staggered-grid and MPFA finite volume methods for free flow/porous-medium flow problems}, volume = 401, year = 2020 }
36. Seitz, G., Helmig, R., & Class, H. (2020). A numerical modeling study on the influence of porosity changes during thermochemical heat storage. Applied Energy, 259, 114152. https://doi.org/10.1016/j.apenergy.2019.114152
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    BibTeX

    @article{Seitz-Seitz-2020-01, author = {Seitz, Gabriele and Helmig, Rainer and Class, Holger}, doi = {10.1016/j.apenergy.2019.114152}, issn = {0306-2619}, journal = {Applied Energy}, month = {02}, pages = 114152, title = {A numerical modeling study on the influence of porosity changes during thermochemical heat storage}, url = {http://www.sciencedirect.com/science/article/pii/S0306261919318392}, volume = 259, year = 2020 }

    Link

    http://www.sciencedirect.com/science/article/pii/S0306261919318392
37. de Winter, M., Weishaupt, K., Scheller, S., Frey, S., Raoof, A., Hassanizadeh, M., & Helmig, R. (2020). The Complexity of Porous Media Flow Characterized in a Microfluidic Model Based on Confocal Laser Scanning Microscopy and Micro-PIV. Transport in Porous Media. https://doi.org/10.1007/s11242-020-01515-9
    • Abstract
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    Abstract

    In this study, the complexity of a steady-state flow through porous media is revealed using confocal laser scanning microscopy (CLSM). Micro-particle image velocimetry (micro-PIV) is applied to construct movies of colloidal particles. The calculated velocity vector fields from images are further utilized to obtain laminar flow streamlines. Fluid flow through a single straight channel is used to confirm that quantitative CLSM measurements can be conducted. Next, the coupling between the flow in a channel and the movement within an intersecting dead-end region is studied. Quantitative CLSM measurements confirm the numerically determined coupling parameter from earlier work of the authors. The fluid flow complexity is demonstrated using a porous medium consisting of a regular grid of pores in contact with a flowing fluid channel. The porous media structure was further used as the simulation domain for numerical modeling. Both the simulation, based on solving Stokes equations, and the experimental data show presence of non-trivial streamline trajectories across the pore structures. In view of the results, we argue that the hydrodynamic mixing is a combination of non-trivial streamline routing and Brownian motion by pore-scale diffusion. The results provide insight into challenges in upscaling hydrodynamic dispersion from pore scale to representative elementary volume (REV) scale. Furthermore, the successful quantitative validation of CLSM-based data from a microfluidic model fed by an electrical syringe pump provided a valuable benchmark for qualitative validation of computer simulation results.

    BibTeX

    @article{de_winter_complexity_2020, abstract = {In this study, the complexity of a steady-state flow through porous media is revealed using confocal laser scanning microscopy (CLSM). Micro-particle image velocimetry (micro-PIV) is applied to construct movies of colloidal particles. The calculated velocity vector fields from images are further utilized to obtain laminar flow streamlines. Fluid flow through a single straight channel is used to confirm that quantitative CLSM measurements can be conducted. Next, the coupling between the flow in a channel and the movement within an intersecting dead-end region is studied. Quantitative CLSM measurements confirm the numerically determined coupling parameter from earlier work of the authors. The fluid flow complexity is demonstrated using a porous medium consisting of a regular grid of pores in contact with a flowing fluid channel. The porous media structure was further used as the simulation domain for numerical modeling. Both the simulation, based on solving Stokes equations, and the experimental data show presence of non-trivial streamline trajectories across the pore structures. In view of the results, we argue that the hydrodynamic mixing is a combination of non-trivial streamline routing and Brownian motion by pore-scale diffusion. The results provide insight into challenges in upscaling hydrodynamic dispersion from pore scale to representative elementary volume (REV) scale. Furthermore, the successful quantitative validation of CLSM-based data from a microfluidic model fed by an electrical syringe pump provided a valuable benchmark for qualitative validation of computer simulation results.}, author = {de Winter, Matthijs and Weishaupt, Kilian and Scheller, Stefan and Frey, Steffen and Raoof, Amir and Hassanizadeh, Majid and Helmig, Rainer}, doi = {10.1007/s11242-020-01515-9}, issn = {1573-1634}, journal = {Transport in Porous Media}, language = {en}, month = {11}, publisher = {Springer Science and Business Media {LLC}}, title = {The Complexity of Porous Media Flow Characterized in a Microfluidic Model Based on Confocal Laser Scanning Microscopy and Micro-{PIV}}, url = {https://doi.org/10.1007/s11242-020-01515-9}, urldate = {2020-11-27}, year = 2020 }

    Link

    https://doi.org/10.1007/s11242-020-01515-9
38. Ghosh, T., Bringedal, C., Helmig, R., & Sekhar, G. P. R. (2020). Upscaled equations for two-phase flow in highly heterogeneous porous media: Varying permeability and porosity. Advances in Water Resources, 145, 103716. https://doi.org/10.1016/j.advwatres.2020.103716
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    BibTeX

    @article{Ghosh2020-01, author = {Ghosh, Tufan and Bringedal, Carina and Helmig, Rainer and Sekhar, G.P. Raja}, doi = {10.1016/j.advwatres.2020.103716}, journal = {Advances in Water Resources}, month = {11}, pages = 103716, publisher = {Elsevier {BV}}, title = {Upscaled equations for two-phase flow in highly heterogeneous porous media: Varying permeability and porosity}, url = {https://doi.org/10.1016/j.advwatres.2020.103716}, volume = 145, year = 2020 }

    Link

    https://doi.org/10.1016/j.advwatres.2020.103716
39. Heck, K., Coltman, E., Schneider, J., & Helmig, R. (2020). Influence of Radiation on Evaporation Rates: A Numerical Analysis. Water Resources Research, 56(10), Article 10. https://doi.org/10.1029/2020WR027332
    • BibTeX
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    BibTeX

    @article{lh2-2020-heck-evaporation, author = {Heck, K. and Coltman, E. and Schneider, J. and Helmig, R.}, doi = {10.1029/2020WR027332}, eprint = {https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2020WR027332}, journal = {Water Resources Research}, month = {10}, note = {e2020WR027332 10.1029/2020WR027332}, number = 10, pages = {e2020WR027332}, publisher = {American Geophysical Union ({AGU})}, title = {Influence of Radiation on Evaporation Rates: A Numerical Analysis}, url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020WR027332}, volume = 56, year = 2020 }

    Link

    https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020WR027332
40. Koch, T., Flemisch, B., Helmig, R., Wiest, R., & Obrist, D. (2020). A multi-scale sub-voxel perfusion model to estimate diffusive capillary wall conductivity in multiple sclerosis lesions from perfusion MRI data. International Journal for Numerical Methods in Biomedical Engineering, 36(2), Article 2. https://doi.org/10.1002/cnm.3298
    • Abstract
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    Abstract

    Abstract We propose a new mathematical model to learn capillary leakage coefficients from dynamic susceptibility contrast MRI data. To this end, we derive an embedded mixed-dimension flow and transport model for brain tissue perfusion on a subvoxel scale. This model is used to obtain the contrast agent concentration distribution in a single MRI voxel during a perfusion MRI sequence. We further present a magnetic resonance signal model for the considered sequence including a model for local susceptibility effects. This allows modeling MR signal-time curves that can be compared with clinical MRI data. The proposed model can be used as a forward model in the inverse modeling problem of inferring model parameters such as the diffusive capillary wall conductivity. Acute multiple sclerosis lesions are associated with a breach in the integrity of the blood-brain barrier. Applying the model to perfusion MR data of a patient with acute multiple sclerosis lesions, we conclude that diffusive capillary wall conductivity is a good indicator for characterizing activity of lesions, even if other patient-specific model parameters are not well-known.

    BibTeX

    @article{Koch-Koch-2020-01, abstract = {Abstract We propose a new mathematical model to learn capillary leakage coefficients from dynamic susceptibility contrast MRI data. To this end, we derive an embedded mixed-dimension flow and transport model for brain tissue perfusion on a subvoxel scale. This model is used to obtain the contrast agent concentration distribution in a single MRI voxel during a perfusion MRI sequence. We further present a magnetic resonance signal model for the considered sequence including a model for local susceptibility effects. This allows modeling MR signal-time curves that can be compared with clinical MRI data. The proposed model can be used as a forward model in the inverse modeling problem of inferring model parameters such as the diffusive capillary wall conductivity. Acute multiple sclerosis lesions are associated with a breach in the integrity of the blood-brain barrier. Applying the model to perfusion MR data of a patient with acute multiple sclerosis lesions, we conclude that diffusive capillary wall conductivity is a good indicator for characterizing activity of lesions, even if other patient-specific model parameters are not well-known.}, author = {Koch, Timo and Flemisch, Bernd and Helmig, Rainer and Wiest, Roland and Obrist, Dominik}, copyright = {This article is protected by copyright. All rights reserved.}, doi = {10.1002/cnm.3298}, issn = {2040-7947}, journal = {International Journal for Numerical Methods in Biomedical Engineering}, language = {en}, number = 2, pages = {e3298}, title = {A multi-scale sub-voxel perfusion model to estimate diffusive capillary wall conductivity in multiple sclerosis lesions from perfusion {MRI} data}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/cnm.3298}, volume = 36, year = 2020 }

    Link

    https://onlinelibrary.wiley.com/doi/abs/10.1002/cnm.3298
41. Koch, T., Helmig, R., & Schneider, M. (2020). A new and consistent well model for one-phase flow in anisotropic porous media using a distributed source model. Journal of Computational Physics, 410, 109369. https://doi.org/10.1016/j.jcp.2020.109369
    • BibTeX

    BibTeX

    @article{Kochetal2020JCPwell, author = {Koch, Timo and Helmig, Rainer and Schneider, Martin}, doi = {https://doi.org/10.1016/j.jcp.2020.109369}, issn = {0021-9991}, journal = {Journal of Computational Physics}, month = {06}, pages = 109369, title = {A new and consistent well model for one-phase flow in anisotropic porous media using a distributed source model}, volume = 410, year = 2020 }
42. Koch, T., Schneider, M., Helmig, R., & Jenny, P. (2020). Modeling tissue perfusion in terms of 1d-3d embedded mixed-dimension coupled problems with distributed sources. Journal of Computational Physics, 410, 109370. https://doi.org/10.1016/j.jcp.2020.109370
    • Abstract
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    Abstract

    We present a new method for modeling tissue perfusion on the capillary scale. The microvasculature is represented by a network of one-dimensional vessel segments embedded in the extra-vascular space. Vascular and extra-vascular space exchange fluid over the vessel walls. This exchange is modeled by distributed sources using smooth kernel functions for the extra-vascular domain. It is shown that the proposed method may significantly improve the approximation of the exchange flux, in comparison with existing methods for mixed-dimension embedded problems. Furthermore, the method exhibits better convergence rates of the relevant quantities due to the increased regularity of the extra-vascular pressure solution. Numerical experiments with a vascular network from the rat cortex show that the error in the approximation of the exchange flux for coarse grid resolutions may be decreased by a factor of 3. This may open the way for computing on larger network domains, where a fine grid resolution cannot be achieved in practical simulations due to constraints in computational resources, for example in the context of uncertainty quantification.

    BibTeX

    @article{Kochetal2020JCP1d3dkernel, abstract = {We present a new method for modeling tissue perfusion on the capillary scale. The microvasculature is represented by a network of one-dimensional vessel segments embedded in the extra-vascular space. Vascular and extra-vascular space exchange fluid over the vessel walls. This exchange is modeled by distributed sources using smooth kernel functions for the extra-vascular domain. It is shown that the proposed method may significantly improve the approximation of the exchange flux, in comparison with existing methods for mixed-dimension embedded problems. Furthermore, the method exhibits better convergence rates of the relevant quantities due to the increased regularity of the extra-vascular pressure solution. Numerical experiments with a vascular network from the rat cortex show that the error in the approximation of the exchange flux for coarse grid resolutions may be decreased by a factor of 3. This may open the way for computing on larger network domains, where a fine grid resolution cannot be achieved in practical simulations due to constraints in computational resources, for example in the context of uncertainty quantification.}, author = {Koch, Timo and Schneider, Martin and Helmig, Rainer and Jenny, Patrick}, doi = {10.1016/j.jcp.2020.109370}, issn = {0021-9991}, journal = {Journal of Computational Physics}, month = {06}, pages = 109370, publisher = {Elsevier {BV}}, title = {Modeling tissue perfusion in terms of 1d-3d embedded mixed-dimension coupled problems with distributed sources}, url = {https://doi.org/10.1016/j.jcp.2020.109370}, volume = 410, year = 2020 }

    Link

    https://doi.org/10.1016/j.jcp.2020.109370
43. Coltman, E., Lipp, M., Vescovini, A., & Helmig, R. (2020). Obstacles, Interfacial Forms, and Turbulence: A Numerical Analysis of Soil-Water Evaporation Across Different Interfaces. Transport in Porous Media, 134(2), Article 2. https://doi.org/10.1007/s11242-020-01445-6
    • BibTeX
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    BibTeX

    @article{lh2-2020-coltman-turbulence, author = {Coltman, E. and Lipp, M. and Vescovini, A. and Helmig, R.}, doi = {10.1007/s11242-020-01445-6}, journal = {Transport in porous media}, month = {07}, number = 2, pages = {275--301}, publisher = {Springer Science and Business Media {LLC}}, title = {Obstacles, Interfacial Forms, and Turbulence: A Numerical Analysis of Soil-Water Evaporation Across Different Interfaces}, url = {https://doi.org/10.1007/s11242-020-01445-6}, volume = 134, year = 2020 }

    Link

    https://doi.org/10.1007/s11242-020-01445-6
44. Weishaupt, K., Terzis, A., Zarikos, I., Yang, G., Flemisch, B., de Winter, D. A. M., & Helmig, R. (2020). A Hybrid-Dimensional Coupled Pore-Network/Free-Flow Model Including Pore-Scale Slip and Its Application to a Micromodel Experiment. Transport in Porous Media, 135(1), Article 1. https://doi.org/10.1007/s11242-020-01477-y
    • BibTeX
    • Link

    BibTeX

    @article{Weishaupt2020, author = {Weishaupt, K. and Terzis, A. and Zarikos, I. and Yang, G. and Flemisch, B. and de Winter, D. A. M. and Helmig, R.}, doi = {10.1007/s11242-020-01477-y}, journal = {Transport in Porous Media}, month = {09}, number = 1, pages = {243--270}, publisher = {Springer Science and Business Media {LLC}}, title = {A Hybrid-Dimensional Coupled Pore-Network/Free-Flow Model Including Pore-Scale Slip and Its Application to a Micromodel Experiment}, url = {https://doi.org/10.1007/s11242-020-01477-y}, volume = 135, year = 2020 }

    Link

    https://doi.org/10.1007/s11242-020-01477-y
45. Shokri-Kuehni, S. M. S., Raaijmakers, B., Kurz, T., Or, D., Helmig, R., & Shokri, N. (2020). Water Table Depth and Soil Salinization: From Pore-Scale Processes to Field-Scale Responses. Water Resources Research, 56(2), Article 2. https://doi.org/10.1029/2019WR026707
    • BibTeX
    • Link

    BibTeX

    @article{doi:10.1029/2019WR026707, author = {Shokri-Kuehni, Salomé M. S. and Raaijmakers, Bernadette and Kurz, Theresa and Or, Dani and Helmig, Rainer and Shokri, Nima}, copyright = {©2020. American Geophysical Union. All Rights Reserved.}, doi = {10.1029/2019WR026707}, eprint = {https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2019WR026707}, issn = {1944-7973}, journal = {Water Resources Research}, month = {01}, number = 2, pages = {e2019WR026707}, title = {{Water Table Depth and Soil Salinization: From Pore-Scale Processes to Field-Scale Responses}}, url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019WR026707}, urldate = {2020-02-13}, volume = 56, year = 2020 }

    Link

    https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019WR026707
46. Bahlmann, L. M., Smits, K. M., Heck, K., Coltman, E., Helmig, R., & Neuweiler, I. (2020). Gas Component Transport Across the Soil-Atmosphere Interface for Gases of Different Density: Experiments and Modeling. Water Resources Research, 56(9), Article 9. https://doi.org/10.1029/2020WR027600
    • BibTeX
    • Link

    BibTeX

    @article{lh2-2020-heck-gas-component-transport, author = {Bahlmann, L. M. and Smits, K. M. and Heck, K. and Coltman, E. and Helmig, R. and Neuweiler, I.}, doi = {10.1029/2020WR027600}, eprint = {https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2020WR027600}, journal = {Water Resources Research}, month = {09}, note = {e2020WR027600 10.1029/2020WR027600}, number = 9, pages = {e2020WR027600}, publisher = {American Geophysical Union ({AGU})}, title = {Gas Component Transport Across the Soil-Atmosphere Interface for Gases of Different Density: Experiments and Modeling}, url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020WR027600}, volume = 56, year = 2020 }

    Link

    https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020WR027600
47. Gläser, D., Flemisch, B., Class, H., & Helmig, R. (2020). Frackit: a framework for stochastic fracture network generation and analysis. Journal of Open Source Software, 5. https://doi.org/10.21105/joss.02291
    • BibTeX
    • Link

    BibTeX

    @article{frackit-2020-glaeser, author = {Gläser, Dennis and Flemisch, Bernd and Class, Holger and Helmig, Rainer}, doi = {10.21105/joss.02291}, journal = {Journal of Open Source Software}, month = {12}, page = {2291}, title = {Frackit: a framework for stochastic fracture network generation and analysis}, url = {https://joss.theoj.org/papers/10.21105/joss.02291}, volume = 5, year = 2020 }

    Link

    https://joss.theoj.org/papers/10.21105/joss.02291
48. Weishaupt, K., Joekar-Niasar, V., & Helmig, R. (2019). An efficient coupling of free flow and porous media flow using the pore-network modeling approach. Journal of Computational Physics: X, 1, 100011. https://doi.org/10.1016/j.jcpx.2019.100011
    • BibTeX
    • Link

    BibTeX

    @article{Weishaupt-Weishaupt-2019-01, author = {Weishaupt, Kilian and Joekar-Niasar, Vahid and Helmig, Rainer}, doi = {10.1016/j.jcpx.2019.100011}, issn = {2590-0552}, journal = {Journal of Computational Physics: X}, month = {01}, pages = 100011, publisher = {Elsevier {BV}}, title = {An efficient coupling of free flow and porous media flow using the pore-network modeling approach}, url = {http://www.sciencedirect.com/science/article/pii/S2590055219300277}, volume = 1, year = 2019 }

    Link

    http://www.sciencedirect.com/science/article/pii/S2590055219300277
49. Yang, G., Terzis, A., Zarikos, I., Hassanizadeh, S. M., Weigand, B., & Helmig, R. (2019). Internal flow patterns of a droplet pinned to the hydrophobic surfaces of a confined microchannel using micro-PIV and VOF simulations. Chemical Engineering Journal, 370, 444–454. https://doi.org/10.1016/j.cej.2019.03.191
    • BibTeX
    • Link

    BibTeX

    @article{Helmig-Yang-2019-01, author = {Yang, Guang and Terzis, Alexandros and Zarikos, Ioannis and Hassanizadeh, S. Majid and Weigand, Bernhard and Helmig, Rainer}, doi = {10.1016/j.cej.2019.03.191}, issn = {1385-8947}, journal = {Chemical Engineering Journal}, month = {08}, pages = {444 - 454}, title = {Internal flow patterns of a droplet pinned to the hydrophobic surfaces of a confined microchannel using micro-PIV and VOF simulations}, url = {http://www.sciencedirect.com/science/article/pii/S1385894719306618}, volume = 370, year = 2019 }

    Link

    http://www.sciencedirect.com/science/article/pii/S1385894719306618
50. Bilke, L., Flemisch, B., Kalbacher, T., Kolditz, O., Helmig, R., & Nagel, T. (2019). Development of Open-Source Porous Media Simulators: Principles and Experiences. Transport in Porous Media, 130(1), Article 1. https://doi.org/10.1007/s11242-019-01310-1
    • BibTeX
    • Link

    BibTeX

    @article{Flemisch-Bilke-2019-01, author = {Bilke, Lars and Flemisch, Bernd and Kalbacher, Thomas and Kolditz, Olaf and Helmig, Rainer and Nagel, Thomas}, day = 01, doi = {10.1007/s11242-019-01310-1}, issn = {1573-1634}, journal = {Transport in Porous Media}, month = {10}, number = 1, pages = {337--361}, title = {Development of Open-Source Porous Media Simulators: Principles and Experiences}, url = {https://doi.org/10.1007/s11242-019-01310-1}, volume = 130, year = 2019 }

    Link

    https://doi.org/10.1007/s11242-019-01310-1
51. Gläser, D., Flemisch, B., Helmig, R., & Class, H. (2019). A hybrid-dimensional discrete fracture model for non-isothermal two-phase flow in fractured porous media. GEM - International Journal on Geomathematics, 10(1), Article 1. https://doi.org/10.1007/s13137-019-0116-8
    • BibTeX
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    BibTeX

    @article{Glaeser-Glaeser-2019-01, author = {Gläser, Dennis and Flemisch, Bernd and Helmig, Rainer and Class, Holger}, doi = {10.1007/s13137-019-0116-8}, issn = {1869-2680}, journal = {GEM - International Journal on Geomathematics}, language = {en}, month = {01}, number = 1, pages = 5, title = {A hybrid-dimensional discrete fracture model for non-isothermal two-phase flow in fractured porous media}, url = {https://doi.org/10.1007/s13137-019-0116-8}, urldate = {2020-01-10}, volume = 10, year = 2019 }

    Link

    https://doi.org/10.1007/s13137-019-0116-8
52. Yang, G., Coltman, E., Weishaupt, K., Terzis, A., Helmig, R., & Weigand, B. (2019). On the Beavers-Joseph interface condition for non-parallel coupled channel flow over a porous structure at high Reynolds numbers. Transport in Porous Media. https://doi.org/10.1007/s11242-019-01255-5
    • BibTeX

    BibTeX

    @article{NULL, author = {Yang, Guang and Coltman, Edward and Weishaupt, Kilian and Terzis, Alexandros and Helmig, Rainer and Weigand, Bernhard}, doi = {10.1007/s11242-019-01255-5}, journal = {Transport in Porous Media}, month = {02}, note = {, IWS2ID=4510 , Partnerinstitution: Institut für Thermodynamik der Luft- und Raumfahrt (ITLR) , Partneraddress: Stuttgart }, title = {On the Beavers-Joseph interface condition for non-parallel coupled channel flow over a porous structure at high Reynolds numbers}, year = 2019 }
53. Zhuang, L., Hassanizadeh, S. M., van Duijn, C. J., Zimmermann, S., Zizina, I., & Helmig, R. (2019). Experimental and Numerical Studies of Saturation Overshoot during Infiltration into a Dry Soil. Vadose Zone Journal, 18(1), Article 1. https://doi.org/10.2136/vzj2018.09.0167
    • BibTeX
    • Link

    BibTeX

    @article{Helmig-Zuang-2019-01, author = {Zhuang, Luwen and Hassanizadeh, S. Majid and van Duijn, C.J. and Zimmermann, Susanne and Zizina, Irina and Helmig, Rainer}, doi = {10.2136/vzj2018.09.0167}, eprint = {https://acsess.onlinelibrary.wiley.com/doi/pdf/10.2136/vzj2018.09.0167}, journal = {Vadose Zone Journal}, month = {05}, number = 1, pages = 180167, title = {Experimental and Numerical Studies of Saturation Overshoot during Infiltration into a Dry Soil}, url = {https://acsess.onlinelibrary.wiley.com/doi/abs/10.2136/vzj2018.09.0167}, volume = 18, year = 2019 }

    Link

    https://acsess.onlinelibrary.wiley.com/doi/abs/10.2136/vzj2018.09.0167
54. Mitra, K., Köppl, T., Duijn, H. van, Pop, I. S., & Helmig, R. (2019). Fronts in two-phase porous media flow problems: the effects of hysteresis and dynamic capillarity. Studies in Applied Mathematics, 1906.08134. https://research.tue.nl/en/publications/fronts-in-two-phase-porous-media-flow-problems-the-effects-of-hys
    • BibTeX
    • Link

    BibTeX

    @article{Helmig-Mitra-2019-01, author = {Mitra, Koondanibha and Köppl, Tobias and Duijn, Hans van and Pop, Iuliu Sorin and Helmig, Rainer}, issn = {0022-2526}, journal = {Studies in Applied Mathematics}, language = {English}, month = {07}, pages = {1906.08134}, publisher = {Wiley-Blackwell}, shorttitle = {Fronts in two-phase porous media flow problems}, title = {Fronts in two-phase porous media flow problems: the effects of hysteresis and dynamic capillarity}, url = {https://research.tue.nl/en/publications/fronts-in-two-phase-porous-media-flow-problems-the-effects-of-hys}, year = 2019 }

    Link

    https://research.tue.nl/en/publications/fronts-in-two-phase-porous-media-flow-problems-the-effects-of-hys
55. Vidotto, Ettore., Koch, Timo., Köppl, Tobias., Helmig, Rainer., & Wohlmuth, Barbara. (2019). Hybrid Models for Simulating Blood Flow in Microvascular Networks. Multiscale Modeling & Simulation, 17(3), Article 3. https://doi.org/10.1137/18M1228712
    • BibTeX
    • Link

    BibTeX

    @article{Koch-Vidotto-2019-01, author = {Vidotto, Ettore. and Koch, Timo. and Köppl, Tobias. and Helmig, Rainer. and Wohlmuth, Barbara.}, doi = {10.1137/18M1228712}, issn = {1540-3459}, journal = {Multiscale Modeling \& Simulation}, month = {01}, number = 3, pages = {1076--1102}, title = {Hybrid {Models} for {Simulating} {Blood} {Flow} in {Microvascular} {Networks}}, url = {https://epubs.siam.org/doi/10.1137/18M1228712}, urldate = {2020-01-10}, volume = 17, year = 2019 }

    Link

    https://epubs.siam.org/doi/10.1137/18M1228712
56. Yang, G., Vaikuntanathan, V., Terzis, A., Cheng, X., Weigand, B., & Helmig, R. (2019). Impact of a linear array of hydrophilic and superhydrophobic spheres on a deep water pool. Colloids and Interfaces. https://doi.org/10.3390/colloids3010029
    • BibTeX

    BibTeX

    @article{NULL, author = {Yang, Guang and Vaikuntanathan, Visakh and Terzis, Alexandros and Cheng, Xin and Weigand, Bernhard and Helmig, Rainer}, doi = {10.3390/colloids3010029}, journal = {Colloids and Interfaces}, month = {01}, note = {, IWS2ID=4566 , Partnerinstitution: Institut für Thermodynamik der Luft- und Raumfahrt (ITLR), Shanghai Jiao Tong University , Partneraddress: }, title = {Impact of a linear array of hydrophilic and superhydrophobic spheres on a deep water pool}, year = 2019 }
57. Terzis, A., Zarikos, I., Weishaupt, K., Yang, G., Chu, X., Helmig, R., & Weigand, B. (2019). Microscopic velocity field measurements inside a regular porous medium adjacent to a low Reynolds number channel flow. Physics of Fluids, 31(4), Article 4. https://doi.org/10.1063/1.5092169
    • BibTeX
    • Link

    BibTeX

    @article{Weishaupt-Terzis-2019-01, author = {Terzis, A. and Zarikos, I. and Weishaupt, K. and Yang, G. and Chu, X. and Helmig, R. and Weigand, B.}, doi = {10.1063/1.5092169}, issn = {1070-6631}, journal = {Physics of Fluids}, month = {04}, number = 4, pages = 042001, publisher = {{AIP} Publishing}, title = {Microscopic velocity field measurements inside a regular porous medium adjacent to a low Reynolds number channel flow}, url = {https://aip.scitation.org/doi/full/10.1063/1.5092169}, urldate = {2020-01-10}, volume = 31, year = 2019 }

    Link

    https://aip.scitation.org/doi/full/10.1063/1.5092169
58. Gao, B., Davarzani, H., Helmig, R., & Smits, K. M. (2018). Experimental and numerical study of evaporation from wavy surfaces by coupling free flow and porous media flow. Water Resources Research. https://doi.org/10.1029/2018WR023423
    • BibTeX

    BibTeX

    @article{NULL, author = {Gao, Bo and Davarzani, Hossein and Helmig, Rainer and Smits, Kathleen M.}, doi = {10.1029/2018WR023423}, journal = {Water Resources Research}, month = {11}, note = {, IWS2ID=4550 , Partnerinstitution: Colorado School of Mines, Bureau de Recherches Géologiques et Minières , Partneraddress: Golden, Colorado, USA, Orléans, Frankreich }, title = {Experimental and numerical study of evaporation from wavy surfaces by coupling free flow and porous media flow}, year = 2018 }
59. Schneider, M., Köppl, T., Helmig, R., Steinle, R., & Hilfer, R. (2018). Stable propagation of saturation overshoots for two-phase flow in porous media. Transport in Porous Media, 121(3), Article 3. https://doi.org/10.1007/s11242-017-0977-y
    • BibTeX
    • Link

    BibTeX

    @article{NULL, author = {Schneider, Martin and Köppl, Tobias and Helmig, Rainer and Steinle, Rouven and Hilfer, Rudolf}, doi = {10.1007/s11242-017-0977-y}, journal = {Transport in Porous Media}, month = {11}, note = {, IWS2ID=4489 , Partnerinstitution: Institut für Computerphysik }, number = 3, page = {621-641}, title = {Stable propagation of saturation overshoots for two-phase flow in porous media}, url = {https://doi.org/10.1007/s11242-017-0977-y}, volume = 121, year = 2018 }

    Link

    https://doi.org/10.1007/s11242-017-0977-y
60. Praditia, T., Helmig, R., & Hajibeygi, H. (2018). Multiscale formulation for coupled flow-heat equations arising from single-phase flow in fractured geothermal reservoirs. Computational Geosciences. https://doi.org/10.1007/s10596-018-9754-4
    • BibTeX

    BibTeX

    @article{NULL, author = {Praditia, Timothy and Helmig, Rainer and Hajibeygi, Hadi}, doi = {10.1007/s10596-018-9754-4}, journal = {Computational Geosciences}, month = {11}, note = {, IWS2ID=4491 , Partnerinstitution: Delft University of Technology }, title = {Multiscale formulation for coupled flow-heat equations arising from single-phase flow in fractured geothermal reservoirs}, year = 2018 }
61. Schneider, M., Gläser, D., Flemisch, B., & Helmig, R. (2018). Comparison of finite-volume schemes for diffusion problems. Oil & Gas Science and Technology – Revue d’IFP Energies Nouvelles, 73. https://ogst.ifpenergiesnouvelles.fr/articles/ogst/pdf/2018/01/ogst180050.pdf
    • BibTeX
    • Link

    BibTeX

    @article{NULL, author = {Schneider, Martin and Gläser, Dennis and Flemisch, Bernd and Helmig, Rainer}, journal = {Oil & Gas Science and Technology – Revue d'IFP Energies nouvelles}, month = {12}, note = {, IWS2ID=4565 , Partnerinstitution: IFP Energies nouvelles , Partneraddress: Rueil Malmaison }, title = {Comparison of finite-volume schemes for diffusion problems}, url = {https://ogst.ifpenergiesnouvelles.fr/articles/ogst/pdf/2018/01/ogst180050.pdf}, volume = 73, year = 2018 }

    Link

    https://ogst.ifpenergiesnouvelles.fr/articles/ogst/pdf/2018/01/ogst180050.pdf
62. Vidotto, E., Helmig, R., Schneider, M., & Wohlmuth, B. (2018). Streamline method for resolving sharp fronts for complex two-phase flow in porous media. Computational Geosciences, 22(6), Article 6. https://doi.org/10.1007/s10596-018-9767-z
    • Abstract
    • BibTeX
    • Link

    Abstract

    In this paper, we present a fast streamline-based numerical method for the two-phase flow equations in high-rate flooding scenarios for incompressible fluids in heterogeneous and anisotropic porous media. A fractional flow formulation is adopted and a discontinuous Galerkin method (DG) is employed to solve the pressure equation. Capillary effects can be neglected in high-rate flooding scenarios. This allows us to present an improved streamline approach in combination with the one-dimensional front tracking method to solve the transport equation. To handle the high computational costs of the DG approximation, domain decomposition is applied combined with an algebraic multigrid preconditioner to solve the linear system. Special care at the interior interfaces is required and the streamline tracer has to include a dynamic communication strategy. The method is validated in various two- and three-dimensional tests, where comparisons of the solutions in terms of approximation of flow front propagation with standard fully implicit finite-volume methods are provided.

    BibTeX

    @article{Vidotto2018, abstract = {In this paper, we present a fast streamline-based numerical method for the two-phase flow equations in high-rate flooding scenarios for incompressible fluids in heterogeneous and anisotropic porous media. A fractional flow formulation is adopted and a discontinuous Galerkin method (DG) is employed to solve the pressure equation. Capillary effects can be neglected in high-rate flooding scenarios. This allows us to present an improved streamline approach in combination with the one-dimensional front tracking method to solve the transport equation. To handle the high computational costs of the DG approximation, domain decomposition is applied combined with an algebraic multigrid preconditioner to solve the linear system. Special care at the interior interfaces is required and the streamline tracer has to include a dynamic communication strategy. The method is validated in various two- and three-dimensional tests, where comparisons of the solutions in terms of approximation of flow front propagation with standard fully implicit finite-volume methods are provided.}, author = {Vidotto, Ettore and Helmig, Rainer and Schneider, Martin and Wohlmuth, Barbara}, day = 01, doi = {10.1007/s10596-018-9767-z}, issn = {1573-1499}, journal = {Computational Geosciences}, month = {12}, number = 6, pages = {1487--1502}, title = {Streamline method for resolving sharp fronts for complex two-phase flow in porous media}, url = {https://doi.org/10.1007/s10596-018-9767-z}, volume = 22, year = 2018 }

    Link

    https://doi.org/10.1007/s10596-018-9767-z
63. Schneider, M., Flemisch, B., Helmig, R., Terekhov, K., & Tchelepi, H. (2018). Monotone nonlinear finite-volume method for challenging grids. Computational Geosciences. https://doi.org/10.1007/s10596-017-9710-8
    • BibTeX
    • Link

    BibTeX

    @article{NULL, author = {Schneider, Martin and Flemisch, Bernd and Helmig, Rainer and Terekhov, Kirill and Tchelepi, Hamdi}, doi = {10.1007/s10596-017-9710-8}, journal = {Computational Geosciences}, month = {01}, note = {, IWS2ID=4426 , Partneraddress: Stanford, California, USA }, title = {Monotone nonlinear finite-volume method for challenging grids}, url = {https://doi.org/10.1007/s10596-017-9710-8}, year = 2018 }

    Link

    https://doi.org/10.1007/s10596-017-9710-8
64. Köppl, T., Fedoseyev, M., & Helmig, R. (2018). Simulation of surge reduction systems using dimensionally reduced models. Journal of Hydraulic Engineering. https://doi.org/10.1061/(ASCE)HY.1943-7900.0001553
    • BibTeX
    • Link

    BibTeX

    @article{NULL, author = {Köppl, Tobias and Fedoseyev, Mikhail and Helmig, Rainer}, doi = {10.1061/(ASCE)HY.1943-7900.0001553}, journal = {Journal of Hydraulic Engineering}, month = {12}, note = {, IWS2ID=4466 , Partnerinstitution: Gubkin Russian State University of Oil and Gas , Partneraddress: Moscow, Russia }, title = {Simulation of surge reduction systems using dimensionally reduced models}, url = {https://ascelibrary.org/doi/10.1061/%28ASCE%29HY.1943-7900.0001553}, year = 2018 }

    Link

    https://ascelibrary.org/doi/10.1061/%28ASCE%29HY.1943-7900.0001553
65. Becker, B., Guo, B., Bandilla, K., Celia, M. A., Flemisch, B., & Helmig, R. (2018). An adaptive multiphysics model coupling vertical equilibrium and full multidimensions for multiphase flow in porous media. Water Resources Research, 54. https://doi.org/10.1029/2017WR022303
    • BibTeX
    • Link

    BibTeX

    @article{NULL, author = {Becker, Beatrix and Guo, Bo and Bandilla, Karl and Celia, Michael A. and Flemisch, Bernd and Helmig, Rainer}, doi = {10.1029/2017WR022303}, journal = {Water Resources Research}, month = {05}, note = {, IWS2ID=4512 , Partnerinstitution: Stanford University, Dept. of Energy Resources Engineering, Princeton University, Dept. of Civil and Environmental Engineering }, page = {4347-4360}, title = {An adaptive multiphysics model coupling vertical equilibrium and full multidimensions for multiphase flow in porous media}, url = {https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2017WR022303}, volume = 54, year = 2018 }

    Link

    https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2017WR022303
66. Köppl, T., Santin, G., Haasdonk, B., & Helmig, R. (2018). Numerical modelling of a peripheral arterial stenosis using dimensionally reduced models and machine learning techniques. International Journal for Numerical Methods in Biomedical Engineering. https://doi.org/10.1002/cnm.3095
    • BibTeX

    BibTeX

    @article{NULL, author = {Köppl, Tobias and Santin, Gabriele and Haasdonk, Bernard and Helmig, Rainer}, doi = {10.1002/cnm.3095}, journal = {International Journal for Numerical Methods in Biomedical Engineering}, month = {12}, note = {, IWS2ID=4481 , Partnerinstitution: Institut für Angewandte Analysis und Numerische Simulation }, title = {Numerical modelling of a peripheral arterial stenosis using dimensionally reduced models and machine learning techniques}, year = 2018 }
67. Koch, T., Heck, K., Schröder, N., Class, H., & Helmig, R. (2018). A new simulation framework for soil-root interaction, evaporation, root growth, and solute transport. Vadose Zone Journal. https://doi.org/10.2136/vzj2017.12.0210
    • BibTeX

    BibTeX

    @article{NULL, author = {Koch, Timo and Heck, Katharina and Schröder, Natalie and Class, Holger and Helmig, Rainer}, doi = {10.2136/vzj2017.12.0210}, journal = {Vadose Zone Journal}, month = {08}, note = {, IWS2ID=4546 }, title = {A new simulation framework for soil-root interaction, evaporation, root growth, and solute transport}, year = 2018 }
68. Gläser, D., Helmig, R., Flemisch, B., & Class, H. (2017). A discrete fracture model for two-phase flow in fractured porous media. Advances in Water Resources, 110. https://doi.org/10.1016/j.advwatres.2017.10.031
    • BibTeX

    BibTeX

    @article{NULL, author = {Gläser, Dennis and Helmig, Rainer and Flemisch, Bernd and Class, Holger}, doi = {10.1016/j.advwatres.2017.10.031}, journal = {Advances in Water Resources}, month = {12}, note = {, IWS2ID=4485 }, page = {335-348}, title = {A discrete fracture model for two-phase flow in fractured porous media}, volume = 110, year = 2017 }
69. Terzis, A., Roumeli, E., Weishaupt, K., Brack, S., Aslannejad, H., Groß, J., Hassanizadeh, S. M., Helmig, R., & Weigand, B. (2017). Heat release at the wetting front during capillary filling of cellulosic micro-substrates. Journal of Colloid and Interface Science. https://doi.org/10.1016/j.jcis.2017.06.027
    • BibTeX

    BibTeX

    @article{NULL, author = {Terzis, Alexandros and Roumeli, Eleftheria and Weishaupt, Kilian and Brack, Stefan and Aslannejad, Hamed and Groß, Joachim and Hassanizadeh, S. Majid and Helmig, Rainer and Weigand, Bernhard}, doi = {10.1016/j.jcis.2017.06.027}, journal = {Journal of Colloid and Interface Science}, month = {05}, note = {, IWS2ID=4458 }, title = {Heat release at the wetting front during capillary filling of cellulosic micro-substrates}, year = 2017 }
70. Gupta, S., Deusner, C., Haeckel, M., Helmig, R., & Wohlmuth, B. I. (2017). Testing a thermo-chemo-hydro-geomechanical model for gas hydrate bearing sediments using triaxial compression lab experiments. https://doi.org/10.1002/2017GC006901
    • BibTeX

    BibTeX

    @article{NULL, author = {Gupta, Shubhangi and Deusner, Christian and Haeckel, Matthias and Helmig, Rainer and Wohlmuth, Barbara I.}, doi = {10.1002/2017GC006901}, month = {07}, note = {, IWS2ID=4474 , Partnerinstitution: Helmholtz-Zentrum für Ozeanforschung, Kiel, Lehrstuhl für Numerische Mathematik, TU München }, title = {Testing a thermo-chemo-hydro-geomechanical model for gas hydrate bearing sediments using triaxial compression lab experiments}, year = 2017 }
71. Becker, B., Guo, B., Bandilla, K., Celia, M. A., Flemisch, B., & Helmig, R. (2017). A pseudo-vertical equilibrium model for slow gravity drainage dynamics. Water Resources Research, 53. https://doi.org/10.1002/2017WR021644
    • BibTeX
    • Link

    BibTeX

    @article{NULL, author = {Becker, Beatrix and Guo, Bo and Bandilla, Karl and Celia, Michael A. and Flemisch, Bernd and Helmig, Rainer}, doi = {10.1002/2017WR021644}, journal = {Water Resources Research}, month = {12}, note = {, IWS2ID=4502 , Partnerinstitution: Stanford University, Dept. of Energy Resources Engineering, Princeton University, Dept. of Civil and Environmental Engineering , Partneraddress: Stanford, California, USA, Princeton, NJ, USA }, page = {10,491-10,507}, title = {A pseudo-vertical equilibrium model for slow gravity drainage dynamics}, url = {http://www.iws.uni-stuttgart.de/publikationen/hydrosys/paper/2017/Becker_et_al-2017-Water_Resources_Research.pdf}, volume = 53, year = 2017 }

    Link

    http://www.iws.uni-stuttgart.de/publikationen/hydrosys/paper/2017/Becker_et_al-2017-Water_Resources_Research.pdf
72. Jabbari, M., Shojaee Nasirabadi, P., Jambhekar, V. A., Hattel, J. H., & Helmig, R. (2017). Drying of a tape-cast layer: Numerical investigation of influencing parameters. International Journal of Heat and Mass Transfer, 108. https://doi.org/10.1016/j.ijheatmasstransfer.2017.01.074
    • BibTeX

    BibTeX

    @article{NULL, author = {Jabbari, Mirmasoud and Shojaee Nasirabadi, Parizad and Jambhekar, Vishal Arun and Hattel, Jesper Henri and Helmig, Rainer}, doi = {10.1016/j.ijheatmasstransfer.2017.01.074}, journal = {International Journal of Heat and Mass Transfer}, month = {10}, note = {, IWS2ID=4394 , Partnerinstitution: Warwick Manufacturing Group, University of Warwick and Dept. of Mechanical Engineering, TU Denmark }, page = {2229-2238}, title = {Drying of a tape-cast layer: Numerical investigation of influencing parameters}, volume = 108, year = 2017 }
73. Yang, G., Weigand, B., Terzis, A., Weishaupt, K., & Helmig, R. (2017). Numerical simulation of turbulent flow and heat transfer in a three-dimensional channel coupled with flow through porous structures. Transport in Porous Media, 120. https://doi.org/10.1007/s11242-017-0995-9
    • BibTeX

    BibTeX

    @article{NULL, author = {Yang, Guang and Weigand, Bernhard and Terzis, Alexandros and Weishaupt, Kilian and Helmig, Rainer}, doi = {10.1007/s11242-017-0995-9}, journal = {Transport in Porous Media}, month = {08}, note = {, IWS2ID=4472 , Partnerinstitution: Institut für Thermodynamik der Luft- und Raumfahrt (ITLR) , Partneraddress: Stuttgart }, page = {01--23}, title = {Numerical simulation of turbulent flow and heat transfer in a three-dimensional channel coupled with flow through porous structures}, volume = 120, year = 2017 }
74. Mejri, E., Bouhlila, R., & Helmig, R. (2017). Heterogeneity effects on evaporation-induced halite and gypsum co-precipitation in porous media. Transport in Porous Media. https://doi.org/10.1007/s111242-017-0846-8
    • BibTeX

    BibTeX

    @article{NULL, author = {Mejri, Emna and Bouhlila, Rachida and Helmig, Rainer}, doi = {10.1007/s111242-017-0846-8}, journal = {Transport in Porous Media}, month = {03}, note = {, IWS2ID=4427 }, title = {Heterogeneity effects on evaporation-induced halite and gypsum co-precipitation in porous media}, year = 2017 }
75. Neuweiler, I., & Helmig, R. (2017). Debates - Hypothesis testing in hydrology: a subsurface perspective. Water Resources Research, 53. https://doi.org/1002/2016WR020047
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    BibTeX

    @article{NULL, author = {Neuweiler, Insa and Helmig, Rainer}, doi = {1002/2016WR020047}, journal = {Water Resources Research}, month = {03}, note = {, IWS2ID=4473 , Partnerinstitution: Institut für Strömungsmechanik und Umweltphysik im Bauwesen, Universität Hannover , Partneraddress: Hannover }, page = {1784-1791}, title = {Debates - Hypothesis testing in hydrology: a subsurface perspective}, volume = 53, year = 2017 }
76. Trautz, A., Illangasekare, T., Rodriguez-Iturbe, I., Heck, K., & Helmig, R. (2017). Development of an experimental approach to study coupled soil-plant-atmosphere processes using plant analogs. Water Resources Research, 53.
    • BibTeX

    BibTeX

    @article{NULL, author = {Trautz, Andrew and Illangasekare, Tissa and Rodriguez-Iturbe, Ignacio and Heck, Katharina and Helmig, Rainer}, journal = {Water Resources Research}, month = {04}, note = {, IWS2ID=4464 , Partneraddress: Golden, Colorado, USA }, page = {3319-3340}, title = {Development of an experimental approach to study coupled soil-plant-atmosphere processes using plant analogs}, volume = 53, year = 2017 }
77. Fetzer, T., Vanderborght, J., Mosthaf, K., Smits, K. M., & Helmig, R. (2017). Heat and water transport in soils and across the soil-atmosphere interface: 2. Numerical analysis. Water Resources Research, 53(2), Article 2. https://doi.org/10.1002/2016WR019983
    • BibTeX

    BibTeX

    @article{NULL, author = {Fetzer, Thomas and Vanderborght, Jan and Mosthaf, Klaus and Smits, Kathleen M. and Helmig, Rainer}, doi = {10.1002/2016WR019983}, journal = {Water Resources Research}, month = {10}, note = {, IWS2ID=4403 , Partnerinstitution: Forschungszentrum Jülich (FZJ), TU Denmark, Colorado School of Mines }, number = 2, page = {1080-1100}, title = {Heat and water transport in soils and across the soil-atmosphere interface: 2. Numerical analysis}, volume = 53, year = 2017 }
78. Vanderborght, J., Fetzer, T., Mosthaf, K., Smits, K. M., & Helmig, R. (2017). Heat and water transport in soils and across the soil-atmosphere interface: 1. Theory and different model concepts. Water Resources Research, 53(2), Article 2. https://doi.org/10.1002/2016WR019982
    • BibTeX

    BibTeX

    @article{NULL, author = {Vanderborght, Jan and Fetzer, Thomas and Mosthaf, Klaus and Smits, Kathleen M. and Helmig, Rainer}, doi = {10.1002/2016WR019982}, journal = {Water Resources Research}, month = {10}, note = {, IWS2ID=4402 , Partnerinstitution: Forschungszentrum Jülich (FZJ), TU Denmark, Colorado School of Mines }, number = 2, page = {1057-1079}, title = {Heat and water transport in soils and across the soil-atmosphere interface: 1. Theory and different model concepts}, volume = 53, year = 2017 }
79. Schneider, M., Flemisch, B., & Helmig, R. (2017). Monotone nonlinear finite-volume method for nonisothermal two-phase two-component flow in porous media. International Journal for Numerical Methods in Fluids, 84(6), Article 6. https://doi.org/10.1002/fld.4352
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    • Link

    BibTeX

    @article{NULL, author = {Schneider, Martin and Flemisch, Bernd and Helmig, Rainer}, doi = {10.1002/fld.4352}, journal = {International Journal for Numerical Methods in Fluids}, month = {01}, note = {, IWS2ID=4354 }, number = 6, page = {352-381}, title = {Monotone nonlinear finite-volume method for nonisothermal two-phase two-component flow in porous media}, url = {https://onlinelibrary.wiley.com/doi/10.1002/fld.4352/full}, volume = 84, year = 2017 }

    Link

    https://onlinelibrary.wiley.com/doi/10.1002/fld.4352/full
80. Fattahi, E., Waluga, C., Wohlmuth, B. I., Rüde, U., Manhard, M., & Helmig, R. (2016). Lattice Boltzmann methods in porous media simulations: laminar to turbulent flow. Computers and Fluids, 140.
    • BibTeX

    BibTeX

    @article{NULL, author = {Fattahi, Ehsan and Waluga, Christian and Wohlmuth, Barbara I. and Rüde, Ulrich and Manhard, Michael and Helmig, Rainer}, journal = {Computers and fluids}, month = {11}, note = {, IWS2ID=4405 }, page = {247-259}, title = {Lattice Boltzmann methods in porous media simulations: laminar to turbulent flow}, volume = 140, year = 2016 }
81. Hommel, J., Ebigbo, A., Gerlach, R., Cunningham, A. B., Helmig, R., & Class, H. (2016). Finding a balance between accuracy and effort for modeling biomineralization. Energy Procedia, 97. https://doi.org/10.1016/j.egypro.2016.10.028
    • BibTeX
    • Link

    BibTeX

    @article{NULL, author = {Hommel, Johannes and Ebigbo, Anozie and Gerlach, Robin and Cunningham, Alfred B. and Helmig, Rainer and Class, Holger}, doi = {10.1016/j.egypro.2016.10.028}, journal = {Energy Procedia}, month = {11}, note = {, IWS2ID=4408 , Partnerinstitution: Montana State University }, page = {379-386}, title = {Finding a balance between accuracy and effort for modeling biomineralization}, url = {http://www.iws.uni-stuttgart.de/publikationen/hydrosys/paper/2016/Hommel_EgyPro_2016.pdf}, volume = 97, year = 2016 }

    Link

    http://www.iws.uni-stuttgart.de/publikationen/hydrosys/paper/2016/Hommel_EgyPro_2016.pdf
82. Gupta, S., Wohlmuth, B. I., & Helmig, R. (2016). Multi-rate time stepping schemes for hydro-geomechanical model for subsurface methane hydrate reservoirs. Advances in Water Resources, 91. https://doi.org/10.1016/j.advwatres.2016.02.013
    • BibTeX

    BibTeX

    @article{NULL, author = {Gupta, Shubhangi and Wohlmuth, Barbara I. and Helmig, Rainer}, doi = {10.1016/j.advwatres.2016.02.013}, journal = {Advances in Water Resources}, month = {05}, note = {, IWS2ID=4370 , Partnerinstitution: Lehrstuhl für Numerische Mathematik , Partneraddress: TU München }, page = {78-87}, title = {Multi-rate time stepping schemes for hydro-geomechanical model for subsurface methane hydrate reservoirs}, volume = 91, year = 2016 }
83. Lindner, F., Nuske, P., Weishaupt, K., Helmig, R., Mundt, C., & Pfitzner, M. (2016). Transpiration cooling with local thermal nonequilibrium: Model comparison in multiphase flow in porous media. Journal of Porous Media, 19. https://doi.org/10.1615/JPorMedia.v19.i2.30
    • BibTeX
    • Link

    BibTeX

    @article{NULL, author = {Lindner, Franz and Nuske, Philipp and Weishaupt, Kilian and Helmig, Rainer and Mundt, Christian and Pfitzner, Michael}, doi = {10.1615/JPorMedia.v19.i2.30}, journal = {Journal of Porous Media}, month = {01}, note = {, IWS2ID=4373 }, page = {131-153}, title = {Transpiration cooling with local thermal nonequilibrium: Model comparison in multiphase flow in porous media}, url = {https://www.dl.begellhouse.com/journals/49dcde6d4c0809db,756c5cb610533dc8,29b3011f079da782.html}, volume = 19, year = 2016 }

    Link

    https://www.dl.begellhouse.com/journals/49dcde6d4c0809db,756c5cb610533dc8,29b3011f079da782.html
84. Jambhekar, V. A., Mejri, E., Schröder, N., Helmig, R., & Shokri, N. (2016). Kinetic Approach to Model Reactive Transport and Mixed Salt Precipitation in a Coupled Free-Flow–Porous-Media System. Transport in Porous Media. https://doi.org/10.1007/s11242-016-0665-3
    • BibTeX

    BibTeX

    @article{NULL, author = {Jambhekar, Vishal Arun and Mejri, Emna and Schröder, Natalie and Helmig, Rainer and Shokri, Nima}, doi = {10.1007/s11242-016-0665-3}, journal = {Transport in Porous Media}, month = {03}, note = {, IWS2ID=4347 }, title = {Kinetic Approach to Model Reactive Transport and Mixed Salt Precipitation in a Coupled Free-Flow–Porous-Media System}, year = 2016 }
85. Gläser, D., Dell’Oca, A., Tatomir, A., Bensabat, J., Class, H., Guadagnini, A., Helmig, R., McDermott, C., Riva, M., & Sauter, M. (2016). An Approach Towards a FEP-based Model for Risk Assessment for Hydraulic Fracturing Operations. Energy Procedia, 97, 387--394. https://doi.org/10.1016/j.egypro.2016.10.030
    • BibTeX
    • Link

    BibTeX

    @article{Glaeser-Glaeser-2016-01, author = {Gläser, D. and Dell’Oca, A. and Tatomir, A. and Bensabat, J. and Class, H. and Guadagnini, A. and Helmig, R. and McDermott, C. and Riva, M. and Sauter, M.}, doi = {10.1016/j.egypro.2016.10.030}, issn = {1876-6102}, journal = {Energy Procedia}, language = {en}, month = {11}, note     = {European Geosciences Union General Assembly 2016, EGU Division Energy, Resources \& the Environment (ERE)}, pages = {387--394}, series = {European {Geosciences} {Union} {General} {Assembly} 2016, {EGU} {Division} {Energy}, {Resources} \& the {Environment} ({ERE})}, title = {An {Approach} {Towards} a {FEP}-based {Model} for {Risk} {Assessment} for {Hydraulic} {Fracturing} {Operations}}, url = {http://www.sciencedirect.com/science/article/pii/S187661021630978X}, urldate = {2020-01-14}, volume = 97, year = 2016 }

    Link

    http://www.sciencedirect.com/science/article/pii/S187661021630978X
86. Baber, K., Flemisch, B., & Helmig, R. (2016). Modelling drop dynamics at the interface between free and porous-medium flow using the mortar method. International Journal of Heat and Mass Transfer. https://www.iws.uni-stuttgart.de/publikationen/hydrosys/paper/2014/SimTech_Preprint_Baber2014.pdf
    • BibTeX
    • Link

    BibTeX

    @article{NULL, author = {Baber, Katherina and Flemisch, Bernd and Helmig, Rainer}, journal = {International Journal of Heat and Mass Transfer}, month = {07}, note = {to appear, IWS2ID=2989 }, title = {Modelling drop dynamics at the interface between free and porous-medium flow using the mortar method}, url = {https://www.iws.uni-stuttgart.de/publikationen/hydrosys/paper/2014/SimTech_Preprint_Baber2014.pdf}, year = 2016 }

    Link

    https://www.iws.uni-stuttgart.de/publikationen/hydrosys/paper/2014/SimTech_Preprint_Baber2014.pdf
87. Hommel, J., Lauchnor, E., Gerlach, R., Cunningham, A. B., Ebigbo, A., Helmig, R., & Class, H. (2016). Investigating the influence of the initial biomass distribution and injection strategies on biofilm-mediated calcite precipitation in porous media. Transport in Porous Media, 114(2), Article 2. https://doi.org/10.1007/s11242-015-0617-3
    • BibTeX
    • Link

    BibTeX

    @article{NULL, author = {Hommel, Johannes and Lauchnor, Ellen and Gerlach, Robin and Cunningham, Alfred B. and Ebigbo, Anozie and Helmig, Rainer and Class, Holger}, doi = {10.1007/s11242-015-0617-3}, journal = {Transport in Porous Media}, month = {12}, note = {, IWS2ID=3133 , Partnerinstitution: Montana State University , Partneraddress: Bozeman, Montana, USA }, number = 2, page = {557-579}, title = {Investigating the influence of the initial biomass distribution and injection strategies on biofilm-mediated calcite precipitation in porous media}, url = {http://rdcu.be/jUty}, volume = 114, year = 2016 }

    Link

    http://rdcu.be/jUty
88. Drzisga, D., Köppl, T., Pohl, U., Helmig, R., & Wohlmuth, B. I. (2016). Numerical modeling of compensation mechanisms for peripheral arterial stenoses. Computers in Biology and Medicine, 70, Article 70.
    • BibTeX

    BibTeX

    @article{NULL, author = {Drzisga, Daniel and Köppl, Tobias and Pohl, Ulrich and Helmig, Rainer and Wohlmuth, Barbara I.}, journal = {Computers in Biology and Medicine}, month = {05}, note = {, IWS2ID=4336 , Partnerinstitution: Lehrstuhl für Numerische Mathematik , Partneraddress: TU München }, number = 70, page = {190-201}, title = {Numerical modeling of compensation mechanisms for peripheral arterial stenoses}, year = 2016 }
89. Fetzer, T., Smits, K. M., & Helmig, R. (2016). Effect of Turbulence and Roughness on Coupled Porous-Medium/Free-Flow Exchange Processes. Transport in Porous Media, 114(2), Article 2. https://doi.org/10.1007/s11242-016-0654-6
    • BibTeX

    BibTeX

    @article{NULL, author = {Fetzer, Thomas and Smits, Kathleen M. and Helmig, Rainer}, doi = {10.1007/s11242-016-0654-6}, journal = {Transport in Porous Media}, month = {04}, note = {, IWS2ID=3053 }, number = 2, page = {395-424}, title = {Effect of Turbulence and Roughness on Coupled Porous-Medium/Free-Flow Exchange Processes}, volume = 114, year = 2016 }
90. Jabbari, M., Jambhekar, V. A., Hattel, J. H., & Helmig, R. (2016). Drying of a tape-cast layer: Numerical modelling of the evaporation process in a graded/layered material. International Journal of Heat and Mass Transfer, 103. https://doi.org/10.1016/j.ijheatmasstransfer.2016.08.073
    • BibTeX

    BibTeX

    @article{NULL, author = {Jabbari, Mirmasoud and Jambhekar, Vishal Arun and Hattel, Jesper Henri and Helmig, Rainer}, doi = {10.1016/j.ijheatmasstransfer.2016.08.073}, journal = {International Journal of Heat and Mass Transfer}, month = {12}, note = {, IWS2ID=4392 , Partnerinstitution: Warwick Manufacturing Group, University of Warwick and Dept. of Mechanical Engineering, TU Denmark , Partneraddress: Coventry, UK and Lyngby, Denmark }, page = {1144-1154}, title = {Drying of a tape-cast layer: Numerical modelling of the evaporation process in a graded/layered material}, volume = 103, year = 2016 }
91. Helmig, R., Hassanizadeh, S. M., & Dahle, H. K. (2016). Foreword. NUPUS: Porous media research has got a brand name. Transport in Porous Media, 114. https://doi.org/10.1007/s11242-016-0736-5
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    BibTeX

    @article{NULL, author = {Helmig, Rainer and Hassanizadeh, S. Majid and Dahle, Helge K.}, doi = {10.1007/s11242-016-0736-5}, journal = {Transport in Porous Media}, month = {07}, note = {, IWS2ID=4390 }, page = {235-236}, title = {Foreword. NUPUS: Porous media research has got a brand name}, volume = 114, year = 2016 }
92. Szymanska, P., Tisler, W., Schütz, C., Szymkiewicz, A., Neuweiler, I., & Helmig, R. (2016). Experimental and numerical analysis of air trapping in a porous medium with coarse textured inclusions. Acta Geophysica, 64.
    • BibTeX

    BibTeX

    @article{NULL, author = {Szymanska, Paulina and Tisler, Witold and Schütz, Cindi and Szymkiewicz, Adam and Neuweiler, Insa and Helmig, Rainer}, journal = {Acta Geophysica}, month = {12}, note = {, IWS2ID=4417 , Partnerinstitution: Gdansk University of Technology und Institut für Strömungsmechanik und Umweltphysik im Bauwesen,Leibniz Universität Hannover }, page = {2487-2509}, title = {Experimental and numerical analysis of air trapping in a porous medium with coarse textured inclusions}, volume = 64, year = 2016 }
93. Hommel, J., Lauchnor, E., Phillips, A., Gerlach, R., Cunningham, A. B., Helmig, R., Ebigbo, A., & Class, H. (2015). A revised model for microbially induced calcite precipitation: Improvements and new insights based on recent experiments. Water Resources Research, 51(5), Article 5. https://doi.org/10.1002/2014WR016503
    • BibTeX

    BibTeX

    @article{Hommel2015a, author = {Hommel, Johannes and Lauchnor, Ellen and Phillips, Adrienne and Gerlach, Robin and Cunningham, Alfred B. and Helmig, Rainer and Ebigbo, Anozie and Class, Holger}, doi = {10.1002/2014WR016503}, journal = {Water Resources Research}, month = {05}, note = {, IWS2ID=3059 , Partnerinstitution: Montana State University , Partneraddress: Bozeman, Montana, USA }, number = 5, page = {3695-3715}, title = {A revised model for microbially induced calcite precipitation: Improvements and new insights based on recent experiments}, volume = 51, year = 2015 }
94. Rybak, I., Magiera, J., Helmig, R., & Rohde, C. (2015). Multirate time integration for coupled saturated/unsaturated porous medium and free flow systems. Computational Geosciences. https://doi.org/10.1007/s10596-015-9469-8
    • BibTeX

    BibTeX

    @article{NULL, author = {Rybak, Iryna and Magiera, Jim and Helmig, Rainer and Rohde, Christian}, doi = {10.1007/s10596-015-9469-8}, journal = {Computational Geosciences}, month = {02}, note = {, IWS2ID=2990 , Partnerinstitution: Institut für Angewandte Analysis und Numerische Simulation }, title = {Multirate time integration for coupled saturated/unsaturated porous medium and free flow systems}, year = 2015 }
95. Schwenck, N., Flemisch, B., Helmig, R., & Wohlmuth, B. I. (2015). Dimensionally reduced flow models in fractured porous media: crossings and boundaries. Computational Geosciences, 19(6), Article 6. https://doi.org/10.1007/s10596-015-9536-1
    • BibTeX
    • Link

    BibTeX

    @article{NULL, author = {Schwenck, Nicolas and Flemisch, Bernd and Helmig, Rainer and Wohlmuth, Barbara I.}, doi = {10.1007/s10596-015-9536-1}, journal = {Computational Geosciences}, month = {09}, note = {, IWS2ID=3141 , Partnerinstitution: Lehrstuhl für Numerische Mathematik , Partneraddress: München }, number = 6, page = {1219-1230}, title = {Dimensionally reduced flow models in fractured porous media: crossings and boundaries}, url = {http://link.springer.com/article/10.1007/s10596-015-9536-1}, volume = 19, year = 2015 }

    Link

    http://link.springer.com/article/10.1007/s10596-015-9536-1
96. Nuske, P., Ronneberger, O., Karadimitriou, N., Helmig, R., & Hassanizadeh, S. M. (2015). Modelling Multi-Phase Flow in a Micro-Model with Local Thermal Non-Equilibrium on the Darcy Scale. International Journal of Heat and Mass Transfer, 88.
    • BibTeX

    BibTeX

    @article{NULL, author = {Nuske, Philipp and Ronneberger, Olaf and Karadimitriou, Nikos and Helmig, Rainer and Hassanizadeh, S. Majid}, journal = {International Journal of Heat and Mass Transfer}, month = {10}, note = {, IWS2ID=2995 }, page = {822-835}, title = {Modelling Multi-Phase Flow in a Micro-Model with Local Thermal Non-Equilibrium on the Darcy Scale}, volume = 88, year = 2015 }
97. Faigle, B., Elfeel, M. A., Helmig, R., Becker, B., Flemisch, B., & Geiger, S. (2015). Multi-physics modeling of non-isothermal compositional flow on adaptive grids. Computational Methods in Applied Mechanical Engineering, 292. https://doi.org/10.1016/j.cma.2014.11.030
    • BibTeX
    • Link

    BibTeX

    @article{NULL, author = {Faigle, Benjamin and Elfeel, Mohamed Ahmed and Helmig, Rainer and Becker, Beatrix and Flemisch, Bernd and Geiger, Sebastian}, doi = {10.1016/j.cma.2014.11.030}, journal = {Computational Methods in Applied Mechanical Engineering}, month = {12}, note = {, IWS2ID=3025 }, page = {16-34}, title = {Multi-physics modeling of non-isothermal compositional flow on adaptive grids}, url = {http://www.sciencedirect.com/science/article/pii/S0045782514004630}, volume = 292, year = 2015 }

    Link

    http://www.sciencedirect.com/science/article/pii/S0045782514004630
98. Tatomir, A., Schaffer, M., Kissinger, A., Hommel, J., Nuske, P., Licha, T., Helmig, R., & Sauter, M. (2015). Novel approach for modeling kinetic interface-sensitive (KIS) tracers with respect to time-dependent interfacial area change for the optimization of supercritical carbon dioxide injection into deep saline aquifers. International Journal of Greenhouse Gas Control, 33. https://doi.org/10.1016/j.ijggc.2014.11.020
    • BibTeX

    BibTeX

    @article{NULL, author = {Tatomir, Alexandru and Schaffer, Mario and Kissinger, Alexander and Hommel, Johannes and Nuske, Philipp and Licha, Tobias and Helmig, Rainer and Sauter, Martin}, doi = {10.1016/j.ijggc.2014.11.020}, journal = {International Journal of Greenhouse Gas Control}, month = {12}, note = {, IWS2ID=3013 }, page = {145-153}, title = {Novel approach for modeling kinetic interface-sensitive (KIS) tracers with respect to time-dependent interfacial area change for the optimization of supercritical carbon dioxide injection into deep saline aquifers}, volume = 33, year = 2015 }
99. Lindner, F., Nuske, P., Helmig, R., Mundt, C., & Pfitzner, M. (2014). Transpiration Cooling with Local Thermal Non-Equilibrium: Model Comparison in Multiphase Flow in Porous Media. Journal of Porous Media.
    • BibTeX

    BibTeX

    @article{NULL, author = {Lindner, Franz and Nuske, Philipp and Helmig, Rainer and Mundt, Christian and Pfitzner, Michael}, journal = {Journal of Porous Media}, month = {04}, note = {accepted, IWS2ID=2927 }, title = {Transpiration Cooling with Local Thermal Non-Equilibrium: Model Comparison in Multiphase Flow in Porous Media}, year = 2014 }
100. Schmid, K. S., Groß, J., & Helmig, R. (2014). Chemical osmosis in two-phase flow and salinity-dependent capillary pressures in rocks with microporosity. Water Resources Research. https://doi.org/10.1002/2013WR013848
     • BibTeX

     BibTeX

     @article{NULL, author = {Schmid, Karen Sophie and Groß, Joachim and Helmig, Rainer}, doi = {10.1002/2013WR013848}, journal = {Water Resources Research}, month = {01}, note = {, IWS2ID=2906 }, title = {Chemical osmosis in two-phase flow and salinity-dependent capillary pressures in rocks with microporosity}, year = 2014 }