Pressure pulsation characteristics of the generating pump-turbine in hydraulic short-circuit mode of a two-unit one-tunnel pumped storage system

The hydraulic short-circuit （HSC） mode in Pumped Storage Systems （PSSs） can achieve overall adjustable input through coordinated control of the output/input of multiple units. However，the system's water flow in this mode deviates from the design conditions，which may induce intense pressure pulsations and threaten the stable operation of the units. To explore the impact of HSC on pressure pulsations within the generating unit，a validated three-dimensional computational fluid dynamics model was employed to simulate the branch pipe and pump-turbine of a prototype two-unit one-tunnel PSS. Using conventional dual-unit generation mode as a control case，comparative analysis reveals that the HSC mode amplifies pressure pulsations，particularly the low-frequency components near the bifurcation，with less impact on high-frequency components or areas further away. The Q-criterion and entropy production analysis indicate that intensive water impact at the bifurcation under the HSC mode triggers large-scale flow separations and massive vortices. These vortices migrate into the pump-turbine，intensifying energy dissipation and ultimately amplifying pressure pulsations. This study elucidates the amplification mechanism of pressure pulsations in the HSC mode，providing a basis for investigating the risks and the corresponding mitigation strategies of this mode.