Numerical Investigation of Modified Semi-Cylindrical Weirs

In this study, the flow characteristics over modified semi-cylindrical weirs (MSCM) were investigated using computational fluid dynamics (CFD) simulations. The simulations included the analysis of flow velocity and pressure distribution, turbulence intensity, and streamline patterns. The numerical results were compared to laboratory observations, and a good agreement was observed. Different turbulence models, including renormalized group (RNG) k-epsilon, standard k-epsilon, k-omega two-equations, and large eddy simulation (LES), were evaluated, and all showed suitable performance in simulating the flow field and hydraulic characteristics. However, the standard k-epsilon model outperformed the other models. The analysis of streamline patterns from upstream to downstream of the weirs showed that the curve of the crest provided an opportunity for the flow to harmonize with the surface of the crest. The downstream ramp guided the streamlines, preventing collision with the downstream slab surface and vorticity formation. Additionally, the results indicated that adding the downstream ramp significantly reduced the turbulence intensity of the flow at the toe of the weirs. The analysis of pressure distribution showed that the flow departed from hydrostatic state when reaching the weir, and the maximum deviation occurred at the crest vertex.