Influence of Slope and the Number of Steps on Energy Dissipation in Stepped Spillway Using Numerical Model

Recently the stepped spillways have been used as an appropriate solution for energy dissipation. In the present study, Siahbisheh dam spillway is simulated by using Computational Fluid Dynamic (CFD), in which the Mixture method and Reynolds Stresses Model (RSM) turbulence model is used. In the first modeling series the over all steppes slope is constant. The number of the steps is increased to 80, in which the step height and length is decreased to 0.51 and 1.53 m, respectively. In another case, by reducing the number of the steps to 30, steps height and length increased to 1.36 and 3.9 m, respectively. In the next modeling series, the steppes slope was changed. By reducing the number of the steps in to 30, spillway slope increased to 330 and the height of the steps increased to 1.36 (step length was 2.1 m). Then by increasing the number of the steps to 80, spillway slope decreased to about 140and the height of the steps decreased to 0.51m (step length was 2.1 m). Results analysis and comparison of the increasing the energy dissipation to 60 steppes case shows that by decreasing the number of the steppes into 30, the energy dissipation decreases. This trend is expected to continue by increasing the steppes number into 80, but it is not. It seems that there is no fixed pattern between the number of the steppes and energy dissipation percentage. It can be said the increasing the number of the steppes and decreasing the slope up to a certain value increases the energy dissipation, and this number would be optimal under certain conditions. Finally it seems that the effect of the slope is considerable, so that the case in which larger number of steppes with a mild slope is closer to the optimum condition of maximum energy dissipation.