Numerical simulation of the unstable flow phenomenon in a pump turbine at the load rejection conditions in turbine mode

Abstract

The governor mechanism fails to work when the pump turbine losses the loads suddenly, and the rotating speed of the runner has a quickly increasing. Additionally the unit will jump to the rotating stall condition. In order to study the internal flow field and pressure fluctuation of the pump turbine with different guide vane opening under the rotating stall conditions, a model type pump-turbine of a pumped-storage power station was set as the research object in this paper. And both of the steady and unsteady numerical simulations were carried out to simulate the flow field of the pump-turbine. The internal flow and pressure fluctuation characteristics in guide vane and runner were analysed under the different guide vane opening. The results show that there is an obvious impact at the leading edge of the runner which resulting in the appearance of vortex under the small guide vane opening. With the increasing of the opening and discharge rate, the circumferential crossflow has developed and extended to the vaneless space which blocked the inlet of the runner and disordered the internal flow of the runner. The vortex structures composed of streamwise vortices, horseshoe vortices. The dominant frequency of vaneless space monitor points are 9fn which influenced by RSI under the small guide vane opening and optimal guide vane opening, and 4.75fn which influenced by vortex at great guide vane opening. The pressure fluctuation on pressure and suction surface are affected greatly by the flow pattern inside the runner, there are a lot of low frequency pressure pulsation. The amplitude of all monitor points increased with the increasing of the flow rate.