Estimation of Relative Energy Loss at Stepped Spillways Skimming Flow Regime

Stepped spillways have become a popular method for handling flood releases. The steps increase significantly the rate of energy dissipation taking place on the spillway face and reduce the size of the required downstream energy dissipation basin. The compatibility of stepped spillways with roller compacted concrete (RCC) and gabionconstruction techniques results in low additional cost for the spillway. The flow over a stepped spillway may be divided into three distinct flow regimes depending upon theflow rate for a given stepped spillway geometry: nappe, transition and skimming flowregimes with increasing flow rates. The skimming flow regime is observed for the largest discharges. The waters skim over the pseudo-bottom formed by the step edgesas a coherent turbulent flow. Beneath the pseudo-bottom some intense recirculation and vertical structures fill the cavities. These recirculation eddies are maintained bythe transmission of shear stress from the mainstream and they contribute significantlyto the energy dissipation down the stepped spillway. Based on a similarity between a turbulent surface jet and the flow over the drop, Chamani et al. (2008), developed amodel by using the theories of the shear layer and fully developed surface jet to estimate the energy loss. In this paper, we proposed analytical model for the estimateof relative energy loss at stepped spillways in skimming flow regime based on Chamani et al. (2008) model. We provide a complete comparison of the result of ourmodel and experimental result of other researchers.

کلیدواژه ها:

Stepped Spillway ، Energy Dissipation ، Skimming Flow Regime ، Turbulent jet