Numerical analysis of flow over stepped spillways

It is well known that in the recent years stepped spillways have gained considerable interest as a cost effective structure to dissipate energy of water flows over the spillway of a dam by reducing the size of dissipating structure at downstream. Flow over stepped spillways is a complicated air-water two-phase flow with a free surface, which can be divided into three flow regimes: skimming flow, nappe flow and transition flow. Therefore, the effect of spillways geometry on developing different flow regimes over stepped spillways of semicircular crest and the rate of energy dissipation under different structural configurations are numerically investigated. In these numerical experiments 27 tests have been done for nine models of flatted stepped spillways. Three different types of step number and three profile slopes, 1:0.75, 1:1 and 1:1.25 are used in the analyses, and for each model three types of discharge low, medium and high are utilized to pass over flat stepped spillways. The simulations were performed by employing RNG κ-ɛ turbulence closure model and a commercial software, FLOW-3D. The numerical results are compared with the experimental data gained from studies in the literature, which exhibited a good agreement. It was found that flow rate is the main factor for occurring different flow regimes and the number of steps is directly affected by the formation of skimming flow. The energy dissipation rate was found to be inversely proportional to the number of steps and flow discharge over stepped spillways.