Study On The Rectification Effect Of The Front Bottom Of Large Diffusion Angle Pump Station

The connecting between the diversion canal and the intake sump is called the forebay of the pumping station.The function of the forebay is to transport the water into the intake sump evenly and smoothly and provide good flow conditions of pump.At the same time,it can provides good water absorption conditions for the pump.The forebay is generally divided into two types:forward inflow forebay and lateral inflow forebay.Improper design of the forebay can cause the instable flow.The instable flow has a serious effect on the flow pattern in the intake sump.It can lead to the performance degradation of pump cavitation and energy and even lead to cavitation and vibration.In addition,reflux may cause local deposition in the forebay.Not only does the deposition affect the flow pattern of the intake sump and the normal work of the pump,but also it reduces the efficiency of the pump device.Therefore,it is significant to take some measures to improve the flow pattern in the forebay for the operation and management of the pumping station.The following measures can be used to improve the flow pattern of the forebay:extending the length of the forebay,adding isolated piers to the forebay,reducing the diffusion angle of the forebay;taking diversion measures such as adding diversion piers,diversion plates,diversion gratings and so on;taking rectifying measures such as setting a bottom sill,a column,a pressure water plate and so on.The rectifying method with a bottom sill in the forebay has the advantages of simple structure,convenient construction,good rectifying effect and small hydraulic loss,so it facilitates use in pumping stations.This paper is based on a large diffusion angle pump station as a prototype,designed a small experimental device.Numerical simulations were performed on the bottoms of different locations and heights,and the distribution of flow velocities of the bottom and surface flow patterns and the inlet section of the inlet pool were compared and the optimal solution was selected.In order to integrally study the influence of the location,height and top width and the shape of the section on the rectifying effect of the bottom sill,10 schemes were selected to carry out the comparison and analysis between the numerical simulation and the model test.Finally,the results of model test and numerical simulation are analyzed and compared.The following conclusions are obtained by analyzing the results of the flow patterns of the bottom and the surface layer and the velocity distribution uniformity of each section.The trapezoidal bottom sill can weaken the residual energy carried by the approach channel and improve the flow pattern of the forebay obviously.The location of the bottom sill has a great influence on the flow pattern in the forebay.Too close or far away from the bottom sill can cause the flow disorder in the forebay and the deterioration of the influent flow.The bottom sill which is located at the 1.37B of the intake sump can obviously improve the flow pattern of the forebay and make the flow to flow into each unit more evenly.The flow pattern of the forebay is better with the height of 0.35 times the depth of water at the bottom sill.The top width of the bottom sill has little effect on the flow pattern in the forebay.So,it is suggested that the trapezoidal bottom sill can be uesd to rectifying with the height of 0.35 times the depth of water at the bottom sill and the location at the 1.37B of the intake sump.