Theoretical, CFD Simulation and Experimental Study to Predict the Flowrate Across a Square Edge Broad Crested Weir Depending on the End Depth as a Control Section

A rectangular broad crested weir is the one mostly used in hydraulic structures for measuring flow rates in open channels and rivers. This study is focused on finding the suitable position of the depth above the weir as control section for estimating the flow rate while avoiding the troubles of approach velocity. It was predicted that the end edge of the weir, as a control section, relates to the critical depth (Y_c) as a function of the end depth (Y_e). To determine the relationship between these, experimental tests were achieved with ten different values of the longitudinal slope. Statistical regression analysis indicated the relationship between Y_c and Y_e as about 1.522. Consequently, a new flow rate formula was derived to estimate the flow over the weir and provided a good agreement with the experimental tests. A 3D ANSYS FLUENT Ver. V.16.1 CFD model was also applied to simulate the problem and verify the equation. The water volume fraction and the stream flow pattern were taken into the consideration. The model was able to simulate the problem with a good accuracy for all cases with a percentage error less than 10% when compared to experimental results. Thus indicating that CFD models could be relied upon for describing complex flows.