Pressure fluctuations characteristics and rotating stall propagation mechanism of a pump-turbine in pump mode

The pump-turbines have to be operated under off-design conditions to maintain the stability of the grid. The rotating stall usually occurs at part load in pump mode, which can cause severe pressure fluctuations and strong vibrations. To understand the pressure fluctuations and the stall cells propagation mechanism within turbine, the Scale adaptive simulation (SST-SAS) turbulence model and unsteady RANS approach were adopted to simulate a mode pump-turbine with different flow rate. The results show that the simulated characteristics curves are in good agreement with the experiment results. The rotating stall occurs in the region from 40% to 80% of the best efficiency point (BEP) flow rate. The stall cells rotating along the circumference and their rotating frequency is 3.3%~8.1% of the runner rotating frequency. The propagation of the stall cells is driven by the growth and the decay of the stall cell. The pressure gradient between the stalled and un-stalled channels make the fluids flow from the stalled channel into the un-stalled channel through the gap between the corresponding guide vane and stay vane, which will increase the flow separations in the un-stalled channel. The growth of flow blockage in the un-stalled channel will make the inflow deviate toward the downstream channel and pressure decrease around the leading edge of the guide vane suction side. Further, the adverse pressure gradient between the leading and the trailing edges of the un-stalled guide vane is enhanced. Consequently, the flow blockage continues to grow until the vortices occupy the entire un-stalled channel. © 2017, China Water Power Press. All right reserved.