Flow Simulation Of The Whole Flow Path In Pump-storage Unit Based On Dynamic Mesh And MOC-CFD Coupling Method

With the increasing demand for stability of power systems,pumped-storage power station has become an indispensable part of China’s power grids due to its ability to cut peak and fill valley,adjust frequency and phase,and handle the emergency of power grids.The pumped-storage units have more complex working conditions than that of conventional hydropower stations,and the operating conditions convert more frequently.At the same time,the "S" and "hump" areas on the full-character curve of the pump-turbine make the flow condition.of the units very complicated,which puts a severe test on the safe and stable operation of the pumped-storage power station,and also brings great difficulties to the simulation of the transition process of the pump-turbine.Firstly,this paper established a three-dimensional physical model of the pump-turbine unit and a one-dimensional MOC model of the diversion pipeline system.Then the threedimensional CFD transient simulation based on field measurement data was performed on the transient process under pump outage condition of the pumped storage unit.The dynamic mesh technology was used to simulate the guide vane closure and the profile was used to define the dynamic boundary conditions of the unit’s inlet and outlet.By comparing the simulation results with the on-site data,the evolution process of the flow field in the unit was analyzed.The result shows that under pump outage condition,the greatest threat to the structural safety of the unit is the pressure difference on the working face of the runner vanes in positive rotation backward flow condition,and the pressure difference between the inner and outer sides of the active guide vanes in reverse rotation backward flow condition.Secondly,the 1-D MOC method was used to simulate the diversion pipeline system,and the 3-D CFD method was used to simulate the internal flow state of the unit.The realtime exchange of data on the coupling boundary was emphasized.This method was used to simulate and analyze the pump outage condition of the pump-turbine in the absence of measured data after the quick-closing valve was installed.The results show that the addition of the quick-closing valve can effectively reduce the reversal rotating speed of the unit and the pressure difference at the working face of the blade in the forward-reverse stage.At the same time,accelerating the closing rate of the guide vanes will make the pressure fluctuations in the draft tube and the volute more severe,and increase the pressure in the volute,which will increase the pressure difference between the inner and outer guide vanes in the reverse flow stage.