Transient hydrodynamic instability during the rapid closing process of the guide vanes of pump turbines under power generation conditions

With the increasing scale of renewable energy grid connection, the regulatory role of pumped-storage hydropower plants in power grid stability has become increasingly crucial. This paper focuses on the transient hydraulic instability caused by the rapid closure of guide vanes during the operating condition for power generation of a pump-turbine. A combination of three-dimensional numerical simulation and experimental verification was used. The closure process of guide vanes was simulated using ANSYS Fluent dynamic mesh function. The entropy production theory was employed to quantify energy loss, and the flow structure and vortex band evolution characteristics were analyzed. The results show that the rapid closure of guide vanes leads to a 60% decrease in the flow coefficient and a 16% increase in the head coefficient. The energy loss in the guide vane area is significantly enhanced, mainly concentrated at the guide vane trailing edge. The radial force fluctuations of the runner are as follows: Radial force coefficient in X direction L Fx has a small fluctuation range, Radial force coefficient in Y direction L Fy has a larger fluctuation range, and the Axial force coefficient L Fz has a small fluctuation range. The vortex band in the draft tube is jointly dominated by rotation and shear. After closure, the shear effect is enhanced. The rapid closure of guide vanes can shorten the time for condition switching and respond quickly to the needs of the power grid. The research on the transient instability of pumped-storage units in this paper provides a theoretical basis for improving the transient response capability and operational stability of the units.