Performance Analysis And Optimization For High-head Pump-turbine Considering The Compressibility Of Water

With the development of new energy and the need of peak load and frequency regulation in power system,the pumped storage power stations in China have a tendency to develop toward high head and large capacity.At present,the design of high-head pump turbine runner in China is mostly in the head region from 200m to 500m.The independent design of runner when the head above 600m is not yet mature in domestic,the cavitation and vibration problems are the major factors restricting the development of high-head pump turbine.In order to solve these problems,the work in this paper aims to explore a method which is suitable for the investigation of cavitation and vibration problem and runner design for high-head pump turbine,and provide technical theoretical support for the development of high-head pump-turbine.The research results obtained have important engineering application values.Related research results are as follows:(1)A state equation of mixture fluid is established based on a barotropic state law,combining with the homogeneous equilibrium modeling approach,a cavitation model considering the compressibility of water is obtained.A pump turbine model tested is built to conduct cavitation test.Considering the compressibility of water,the effects on the performance prediction are exploratory investigated.It is found that cavitation simulation method considering the compressibility of water can accurately predict the pump efficiency and cavitation morphology on the surface of blades,the error of pump efficiency within 1%,and the change law of efficiency with cavitation number exactly the same as that of model cavitation test,and the pressure pulsations of measuring points show more abundant features when simulation considering the compressibility of water.(2)The difference in the "S" characteristics of the pump turbine is calculated by comparing the compressible and the incompressible simulation method.The results show that the compressibility of water has great influence of internal flow field characteristics at the special operating conditions(runaway condition,braking and reverse pump condition).Comparing to the model test results,the "S" shape characteristics of pump turbine computed by the compressible simulation is more accurate than that computed by the incompressible simulation.Moreover,more abundant pressure pulsation characteristics can be captured when simulation considering the compressible of water.(3)The flow characteristics of high-head pump turbines under different working conditions were investigated by considering the compressibility,the formation mechanism and the induced pressure field changes of the water blocking are revealed.By investigating the water blocking phenomenon among different runner blade and the frequency characteristics of pressure pulsation caused by water blocking,the nature reasons of unstable problems in high-head pump turbine were reveled.The reason of unstable and vibration phenomenon under 70%output turbine condition was clarified.(4)The influence of the runner geometric parameters on the cavitation and vibration characteristics of the pump turbine was analyzed.The mapping relationship between the geometric parameters of runner and the performance was established.And the compressible flow solution was combined with the runner optimization strategy.The design and optimization program for high-head pump turbine runner with compressibility were developed to seek the reasonable high and low pressure side-loading angles and load distribution on the surface of the blades.The multiple contradictions in the design of the turbine runner and the design of the pump runner were solved.The balance between pumping and power generation was achieved,and a high-head pump turbine runner with superior overall performance was designed.