Experimental Research On Hydraulic Characteristics Of Stilling Basins Of Stepped Spillways

In order to seek for a cheap and efficient measure to increase the energy dissipation rate of the stepped spillway, a new design is provided in which exchanges arc section for a series of steps at the toe of the stepped spillway. The method of model test is used to study the hydraulic characteristics of stilling basins of stepped spillways.According to the gravity similarity rule, an experimental model is designed under different chute angles(40°,50°,60°) ,step heights(4cm, 8cm,16cm)and different forms of hydraulic jump when unit discharge varies from 0.022m~3/s.m to 0.220 m~3/s.m. In this paper, new datas are presented on the characteristics of hydraulic jump, energy dissipation rate and development of the pressure intensity along the floor of the stilling basin next to the chute.A kind of rebound flow can be observed on the head part of the stilling basin if stepped chute is connected with horizontal stilling basin directly which could increase the turbulent intensity in the area of hydraulic jump effectively. The length of critical hydraulic jump becomes shorter under the influence of the rebound flow and stepped chute. We also find that the length of submerged hydraulic jump(the submergence ratio=1.10) is shorter than the length of critical hydraulic jump. In order to describe the rebound flow and the length of critical hydraulic jump, new empirical formula is proposed in this paper.It is an effective measure to improve energy dissipation rate of hydraulic jump formed in the stilling basin which connects the stepped chute without the arc section. The energy dissipation rate of critical hydraulic jump could exceed 60%, which results in that the mean velocity in the downstream only accounts for 10% of that in the upstream of the hydraulic jump. The entire energy dissipation rate of stepped spillway and stilling basin is more than 80%. Though it decreases a little with the discharge increasing, it still has good energy dissipation results.The characteristics of the pressure intensity along the stilling basin floor varies in different areas: Firstly, the maximum volume of the mean pressure, turbulence intensity and peak pulsation pressure can be found in the water flow impact area simultaneously. Secondly, the development of mean pressure and turbulence intensity fluctuation at the upstream of the hydraulic jump, minimum mean pressure volume can be found in this area. Under such circumstances, the minimum mean pressure in this area could be a minor negative one with the remote-motivated hydraulic jump. Thirdly, the volume of mean pressure, turbulence intensity and peak pulsation pressure converge to its mean volume respectively at the downstream of the hydraulic jump. In this paper, new empirical formula for the distribution of the pressure intensity along the stilling basin, distributing rules about peak pressure intensity and the dominant frequency section in the stilling basin can be seen as references for designing stilling basins of stepped spillways.