The Flow Characteristics Investigation of the S-Shaped Region for Pump-Turbine in Small Guide Vane Opening

Pumped-storage power station is the most effective regulator in the current power grid. Its core components, pump turbine, requires higher stability and flexibility. But the two unstable regions, which are the S-Shaped characteristic region of the turbine mode and the hump area of the pump mode, become a bottleneck restricting the development of pump turbine and its system. The two unstable regions are also one of the key issues affecting the safety of units and power system. This paper takes a pump-turbine model of a pumped-storage power station as the research object, and conducts a numerical simulation study on the flow characteristics in the S-Shaped characteristic region of the small guide vane opening. By analyzing the flow streamlines and velocity distributions of different span-wises in the runner, it is found that when the pump turbine is operating at partial operating conditions, a vortex structure is formed on the hub side of the runner, a water ring is formed on the middle span-wise, and the back flow forms on shroud side. When the unstable flow structure appears in the runner, the high axial and circumferential velocity appears at the inlet of the runner and larger range of low speed areas appear in the runner passages. The inflow of the runner is obstructed. When the water ring appears on the middle span-wise, the flow around the head of the runner is serious.