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Institut für Wasser- und Umweltsystemmodellierung - IWS



"Identifying Turbulent Flow Characteristics Using PIV Measurements"

Generally, most flow types in the nature are turbulent. Due to complexity and three dimensional behavior of turbulent ow, identifying its characteristics has high significance in hydraulic engineering. Implementation of computational modeling for turbulent flow is not as simple as for laminar ow. Therefore, experimental studies are conducted to improve our perception of turbulent ow in order to find out its characteristic. Many types of methods are available to do measurements on turbulent ow. Particle image velocimetry (PIV) which is an optical method for ow visualization and velocity measurement in fluid is used for conducting experiments in this thesis. During implementation of this method, ow is seeded with tracer particles of certain size which are able to follow the dynamic of the flow. In the following, ow is illuminated with a light sheet, which is provided by laser in order to make particle visible inside the fluid. Next, a specific camera records the motion of the particles. Given to the motion of the tracer particles and defined time intervals, velocity and direction of the flow is computed. Based upon velocity, other characteristics of the flow are calculated. This study presents the relationship between various discharges and depths and in consequence different ow conditions with different Reynolds and Froude numbers on turbulent flow characteristics. Experimental programs are investigated in this study inside a recirculated flume above the bed and inside the bed in order to find out their influences on average velocity, turbulent kinetic energy, Reynolds stress, shear stress and vorticity as turbulent flow characteristics. In surface flow direct relationship between discharge and velocity and reverse relationship between depth and velocity derived using particle image velocimetry. In consequence, other flow characteristics also show a relatively similar behavior to velocity. In subsurface flow, in addition to finding turbulent flow characteristics in different cases, a comparison between a specific case, which implemented using EPIV and PIV is done with reliable results.