Numerical Simulation Study On Shape Optimization Of Stilling Basin With Sudden Expansion And Drop Sill

With the improvement of people’s awareness of environmental protection,stilling basin with sudden expansion and drop sill was proposed as a dissipator which can be used in highhead,large-unit discharge and environment-friendly engineering.The existence of drop sill and sudden expansion can increase the energy dissipation rate and reduce the bottom hydraulic index effectively,and it also causes the complicated flow field in the stilling basin,the velocity and pressure distribution characteristics of the floor will change,affecting the safety and stability of the stilling basin and hydraulic engineering.In this paper,based on the model tests,numerical simulation and theoretical analysis,the flow pattern,bottom flow velocity,time average pressure and energy dissipation characteristics of the stilling basin with sudden expansion and drop sill were studied with different shape parameters.Based on the results,the optimal shape parameters of the stilling basin were obtained,which can provide references for engineering projects.The main research results and conclusions are as follows:(1)Expressions of the stilling basin with sudden expansion and drop sill were obtained for the sudden expansion ratio based on the momentum and energy equations.The results show that the sudden expansion ratio can be preliminarily calculated for specific projects according to the inlet angel,the height of the drop sill and the Froude number of entering section and the upstream and downstream water levels.(2)According to the results from numerical simulation,the flow characteristics in the stilling basin with sudden expansion were obtained under different shape parameters such as sudden expansion ratio,height of the drop sill,and inlet angle.Taking the submerged underflow as the control flow state,the recommended range of shape parameters was determined,that is,the sudden expansion ratio was set in the range of 1.0～1.6,the relative drop height was in the range of 0.065 ～ 0.13,and the inlet angle was not less than 14°.(3)Based on numerical simulation,the effects of shape parameters such as sudden expansion ratio,height of drop sill,and inlet angle on the maximum bottom flow velocity,side wall flow velocity,and time average pressure were calculated.On the basis of ensuring the stability of flow pattern,with the bottom flow velocity as the control condition,the range of shape parameters of the stilling basin was optimized,that is,the sudden expansion ratio was1.4,the relative drop height was 0.13,and the inlet angle was in the range of 14°～ 16°;Taking the time averaged pressure as the control condition,the shape parameters of the stilling basin was selected,that is,the sudden expansion ratio was 1.6,the relative drop height was 0.13,and the inlet angle was in the range of 14°～ 16°.(4)The energy dissipation rate of the stilling basin under different shape parameters was calculated,and the results show that the energy dissipation rate of the stilling basin with sudden expansion and drop sill was basically above 70%,with good energy dissipation effect.The inlet angle had the most significant impact on the energy dissipation rate,while other parameters had less impact on it.To sum up,on the basis of ensuring the submerged underflow flow pattern,from the perspective of the hydraulics index of the bottom plate and the energy dissipation rate,the shape parameters range of the stilling basin with sudden expansion and drop sill was finally optimized,that is,the sudden expansion ratio was 1.4～1.6,the relative drop height was 0.13,and the inlet angle was 14 °～16 °.