Flow measurement in open channels by combined use of free surface PİV and CFD

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2016
Gharahjeh, Siamak
Stream discharge measurement in open channels is of great importance in hydraulic engineering. For many years, classical devices such as propellers, current meters and weirs have been used for this purpose. In recent times, non-intrusive methods such as PIV (Particle Image Velocimetry) and PTV (Particle Tracking Velocimetry) have been very popular as they are more practical and convenient to automatically collect water free surface velocity which is further analyzed for discharge measurement. Image processing, or so called PIV as a generic name, has been used in this study with the same aim. Extensive set of experiments are carried out in a tilting channel of both rectangular and compound cross section for discharge measurement with the assistance of measured free surface velocity. Experiments are conducted to measure instantaneous velocities of a number of points on the water free surface across the channel width by PTV application for various flow conditions. Sometimes, entire velocity distribution has also been measured by PIV on the free surface. Technical issues regarding tracer particle size and type, travel distance, lighting, recording speed, camera position, image distortion and state of flow are discussed and useful recommendations are suggested. Experimental measurements are used to validate the mathematical model (numerical model) of the problem. Validation includes the calibration of numerical free surface velocity via employment of experimental measurements. This phase obliges the introduction of a new parameter into the numerical model, named as surface vi damping parameter. Last important aspect of the research is the inverse estimation of wall roughness in addition to discharge when free surface velocity, flow cross section and channel bed slope are given inputs.

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Citation Formats
S. Gharahjeh, “Flow measurement in open channels by combined use of free surface PİV and CFD,” Ph.D. - Doctoral Program, Middle East Technical University, 2016.