Numerical Simulation of Flow over Stepped Spillways with varying Step-Angle

In the present study, the flow over the stepped spillway was numerically investigated by using Flow3D model. The effect of step angle on different properties of Nappe flow regime such as the water surface profile, location of free-surface aeration inception, Froude number at the spillway’s toe, and pressure, flow velocity, air concentration and cavitation index were evaluated. The realizable k–e was applied as the turbulence model, and Volume of Fluid (VOF) model was used to determine the free surface flow profiles of the spillway. The model was verified using experimental data. In order to investigate the different characteristics of Nappe flow regime, 17 numerical runs was designed, in which,four step angles, four flow discharge were considered to investigate the flow characteristics over the stepped spillway. The results indicated that the numerical model is well suited with the experimental data over the stepped spillway (RMSE = 0.147 and ARE = 6.9%). In addition, with increasing the step angles, the aeration inception point is generally moved downstream. By increasing the step angles from zero to 10 degrees, the Froude number does not change significantly, however, at the angle of 15 degrees, the Froude number decreases by about 42 percent.