Abstract: To improve the operational stability of pump-turbines for wide-load conditions, the influence of the runner blade angle at the high-pressure edges on performance is examined. A detailed analysis of flow characteristics and vortex structures at three blade angles (zero, positive, and negative inclination) for both optimal and low-flow conditions is conducted. Results show that at the optimal operating point, three blades at different angles all feature insignificant differences in performance, while flow instability develops for low-flow conditions because the increased positive incidence angle at the runner inlet leads to severe flow separation on the blades’ suction sides. Additionally, certain axial vortex structures in the runner passage induce backflow, while the negative inclination angle effectively reduces vortex intensity and suppresses backflow, increasing the spacing between dual axial vortices, mitigating vortex interaction, and thereby reducing energy dissipation. Furthermore, low-frequency components of the vortex structure are weakened significantly, contributing to pressure pulsation suppression to a certain extent. Compared to zero and positive inclination angles, the negative angle helps broaden the operational range of pump-turbines in the turbine mode and enhances operational stability.

Key words: pump turbine, wide-load operation, blade inclination angle, runner vortex, entropy production, pressure fluctuation