Pressure Fluctuations In The "S-shaped" Region Of Pump-turbine

Compared with conventional hydropower stations,pumped storage power stations have the advantages of valley adjustment,peak adjustment,phase adjustment,and accident reserve.They are an indispensable and important part of the country’s power system.As the main power component of pumped-storage power stations,pump-turbines need to adapt to the changes in grid load through frequent conversion of operating conditions.Repeated working condition conversion makes the pump-turbine run more in the "S" zone operating conditions which deviate from the designed working conditions.When the unit operates in this working area,it is easy to operate under the conditions of the turbine,braking and reverse pump,switch back and forth.At this time,the flow and speed of the unit will oscillate,accompanied by strong pressure pulsation,which makes the entire system in an unstable state,causing the unit to fail to start.In severe cases,the structure of the unit will be damaged,which will affect the operation safety of the entire power station.Therefore,the study of the pressure pulsation characteristics of the pump-turbine in the "S" area is of great significance to the safe operation of pumped storage power stations.In this paper,the pressure pulsation characteristics of the pump-turbine in the "S" zone operating conditions are studied by using a combination of experimental testing and numerical simulation.The model test mainly studies the pressure pulsation at different positions of the flow channel under different operating conditions.The results show that the pressure pulsation amplitude in the leafless region is the largest under the same working condition,and the pressure pulsation is closely related to the unit flow and speed.It was found that within a certain range,under the same unit flow rate,with the increase of the unit speed,the pressure pulsation amplitude in the leafless region also increases accordingly,and the increase amplitude shows an upward trend;With the increase unit flow rate,The amplitude of pressure pulsation in the leafless area decreases first and then increases under the same unit speed condition,Meanwhile,the unsteady simulation for the flow in the pump-turbine with 19 mm guide vane opening was carried out by using ANSYS CFX.The pressure fluctuation and internal flow in the vaneless space were analyzed under four typical working conditions.The results show that the flow separation near the blade suction surface is weak under the turbine condition of P01,as well as the pressure fluctuation in vaneless space.Under the runway condition of P05,the flow separation is intensified,which leads to the forming of obvious vortex and the increase of pressure fluctuation.Under the braking condition of P07,the obvious rotating stall with the frequency of 0.7fn is occurred.Moreover,the obvious asymmetric flow is appeared and the high difference of flow rate in each flow channel is occurred,which results in the further increase of pressure fluctuation.However,under the small flow condition of P09,the rotating stall disappears and the flow becomes symmetry,resulting in the small pressure fluctuation.Overall,this study can provide a reference for the optimal design of pump-turbine.