Research on the evolution law and energy loss characteristics of rotating stall in a pump-turbine under pump mode

Under the dual background of global energy transformation and environmental protection, pumped storage is a key energy storage technology to maintain the reliable operation of power systems. As the core component of pumped storage power plants, the operation stability of pump-turbine is of great importance. However, frequent operating condition transitions can trigger rotating stall in pump-turbine under off-design conditions, which seriously affects the energy conversion efficiency and stable operation of the unit. In this study, the pump-turbine model of a certain power plant is taken as research object. A combination of experiment and unsteady simulation is used to thoroughly investigate the mechanism of rotating stall in pump-turbine under pump mode. The circumferential evolution law of rotating stall and the reasons for its disappearance are analyzed in detail. The associated energy conversion characteristics are also elucidated, including pressure fluctuations, turbulent kinetic energy, and entropy production rate. The results show that rotating stall mainly occurs in the guide vane. As the flow rate decreases, the location of rotating stall shifts towards the guide vane inlet and the number of stall cells generally shows a decreasing trend. The circumferential evolution of rotating stall is primarily due to the blockage of stalled channels, which induces flow deflection and alters the adverse pressure gradient within the channels. This drives the front end of stall vortices to move along the runner rotation direction into the next non-stalled channel, while the rear end of the stall vortices exits the stalled channel, resulting in the formation of rotating stall. Additionally, from the perspective of energy loss, the uneven flow state distribution at the runner outlet is an important reason for the disappearance of rotating stall under the valley condition Op3 in hump region. This study further expands the understanding of the mechanism of rotating stall in pump-turbines, and provides important bases for optimization design and operation control of pump-turbines.