Hydraulic Optimization Research And Transient Flow Analysis Of Diversion Bifurcated Pipes In Hydropower Stations

Combined water supply is often used in high head pumped storage power stations.The bifurcated pipe at the end of the diversion system becomes an essential structural form for water supply to each unit.Its structure is not only complex,but also the flow pattern in the pipe is disordered during operation,and the head loss is large.Therefore,the research on the hydraulic optimization characteristics of bifurcated pipe structure has become a hot topic.In addition,due to the special role of pumped storage power station in the power production,it will frequently switch between generating,pumping and regulating conditions,and the transient flow in the pipe will inevitably produce water hammer phenomenon.In order to operate the diversion system of high head pumped storage power station efficiently,the analysis of transient flow characteristics in the pipe becomes the research focus.In this paper,the diversion pipe of a pumped storage power station in China is taken as the research object.Four kinds of three-dimensional models of cone angle are established for the bifurcated pipe section of the diversion system.The three-dimensional steady numerical calculation is carried out to study the influence of the structure of the bifurcated pipe transition section on the flow pattern and to seek the most reasonable cone angle of the transition section.In order to analyze the transient flow characteristics in the bifurcated pipe,the method of one-dimensional MOC and three-dimensional CFD is used to calculate the three-dimensional unsteady flow in part of the diversion pipe.The research and analysis of the hydraulic characteristics of the bifurcated pipe structure show that the increase of the cone angle of the transition pipe can effectively improve the flow situation in the bifurcated pipe,including the reduction of the area of the relatively low pressure area and the return area of the bifurcated pipe interface,and the decrease of the local head loss,which provides a reference for preventing the local cavitation and structural optimization of the bifurcated pipe.In the study of three-dimensional transient flow of water diversion pipeline,the MOC method and CFD method are combined to consider the propagation of water hammer wave in the pipe during valve closing,which can well show the actual flow in the pipe during valve closing,and analyze and compare the velocity and pressure distribution at different valve closing times under three working conditions,as well as the change data of pressure value at the monitoring point,and summarize the use of symmetrical branch valve closing can weaken the hydraulic interference problem.It is preliminarily considered that this method is feasible and provides a new idea for the study of unsteady flow in large projects.