Study of uniformity of flow rate at bilateral water intakes of a broad-crested weir in a channel bend

Construction of weirs in river bends results in the poor performance of intake structures on both sides of the river. The hypothesis for consistent distribution of flow across a bend is the uniformity of unit flow rate over the weir via the change of the spillway-crest profile from horizontal to sloping crest. The main aim of the present study was to simulate flow pattern upstream of sharp- and broad- crested weirs across a 90- degree laboratory channel bend, using FLOW-3D model. The simulation results were compared with corresponding 32 test results from independent physical model and from FLUENT model studies. The stability and sensitivity analysis was carried out to set up for the turbulence model, turbulent mixing length, roughness height, numerical grid sizes, and run time. The RNG turbulence model was better adopted; the turbulent mixing length was about 7% of head water over the weir crest; the size of numerical grids was optimized with 0.02 m; and the run time was about 60 seconds. Modeling results were not sensitive to the turbulent mixing length and roughness heights of the channel. The results indicated that horizontal crested weirs are sufficient outside the bend. Sloping crest weirs provide better convergence of the unit flow rates across the bend in sections between 30 and 60 degrees. It was proved that the slope of the weir crest is to be in the range of 2º to 5º toward the outer bank of the bend. The broad-crested weirs are superior within the channel bend.