Numerical and experimental Study of the influence of Wedge Elements on Hydraulic Parameters and Energy dissipation over stepped spillway in the skimming flow regime

A stepped spillway is a hydraulic and cost effective measure to dissipate the energy of large water flow over the spillway. Due to some limitations in stepped spillways, this study is intended a plan to increase and improve the effectiveness of energy depreciation. For this purpose, the effect of the wedge-shape elements on the velocity and pressure changes over the steps, water level and energy dissipation at downstream the stepped spillway are evaluated. In this regard, several forms of wedge elements are studied with changes in wedge arrangement and the rate of discharge by using numerical model of Flow-3D, and the appropriate models from the aspect of the most energy depreciation are selected and studied in the laboratory. In the laboratory, 25 experiments were performed on 5 physical models.Numerical and experimental results show that the addition of wedge elements on the stepped spillway has reduced the velocity and water depth at downstream of spillway to about 80% and 30%, respectively, and the energy dissipation over the stepped spillway increased by about 2.7 times. Also, by drawing the distribution profiles of pressure on the edge and the floor of steps, it was observed that the negative pressure in the horizontal section turned into a positive pressure. Also negative pressure in the vertical section decreased up to 96% and positive pressure increased about 2 times. As well as, by increasing the density of the elements, the results that increase the energy dissipation are more remarkable.