Research on flow and pressure pulsation characteristics in the S-shaped characteristic region of pump-turbine based on C-shaped blade design

The pump-turbine, as the core equipment of pumped storage power stations, must frequently pass through the S-shaped characteristic region during operation, which severely impacts the stability of the unit. To enhance the operational stability of the pump-turbine in the S-shaped characteristic region, a new runner with C-shaped blades was designed based on an existing runner model. A systematic comparison was conducted on the flow and pressure pulsation characteristics within the S-shaped characteristic region between the flow passage of the C-shaped blades and the original design. The results demonstrate that under braking conditions, the C-type runner exhibits optimal flow stability, with a more uniform streamline distribution in the guide vane and runner domains, and minimal influence from draft tube backflow. Vortex analysis indicates that the C-type runner possesses superior vortex control capability in the guide vane domain, vaneless region, and draft tube compared to the original model. Under reverse pump conditions, the pressure pulsation of the C-type runner is significantly improved; the growth of pulsation amplitude within the blade passage slows, and the maximum pulsation amplitude in the draft tube is reduced by 28% compared to the original model, with an average reduction of 9.8% across all monitoring points. This indicates that the C-type runner can effectively suppress flow instability and pressure pulsation under complex operating conditions. The findings provide an effective technical approach for improving the stability of pump-turbines in the S-shaped characteristic region.