Experimental and numerical study of flow over a broad-crested weir under different hydraulic head ratios

Herein, the free surface flow over a broad-crested weir under different hydraulic heads was investigated. A series of experiments were conducted in a 5-m-long-flume to measure the 3D velocity profile around a rectangular weir using Acoustic Doppler Velocimetry (ADV). The efforts were undertaken to simulate the hydrodynamic field over the weir using open-source toolbox OpenFOAM with five turbulence models including standard k-epsilon, RNG k-epsilon, realizable k-epsilon, k-omega SST and LRR. The numerical results were compared to the experimental data obtained from laboratory measurements. It demonstrated that the k-omega SST and LRR models had the best performance in cases dealing with vortices. Then, separation zone patterns at three locations: behind, over and in front of the weir under different head ratios were examined. It was found that changing the head ratio does not have a notable effect on the relative dimension of separation flow over the weir, whereas the separation zone located behind and in front of the weir grew linearly. After raising the head ratio, the downstream separation zone was split into two significant vortices rotating oppositely. Discharge coefficients are calculated for a wide range of head ratios. It was concluded that Cd equaled 0.85 for head ratios up to 0.3 and then grew to 1.0 by increasing the head ratio.