Influence of the Blade Lean Angle on Fluid-Dynamic Behaviour at Deep Partial Load in a Reversible Pump Turbine

In recent years, reversible pump turbines (RPTs) have become the preferred choice for Pumped Hydro Energy Storage (PHES) systems due to their cost-effectiveness, availability, and adaptability to diverse hydraulic conditions. As intermittent renewable energy sources become more integrated, PHES facilities must expand their operational range and achieve rapid power ramp rates to ensure grid stability. Consequently, RPTs frequently start, stop, and operate at partial loads, leading to instabilities, particularly near runaway conditions. These instabilities may re-strict operational flexibility and prolong synchronization and switching times. Research suggests that an appropriate blade lean angle may help mitigate these instabilities, particularly by reducing rotating stalls, though the underlying mechanisms are not yet fully understood. This paper investigates the influence of blade lean angle on the hydrodynamic stability of a reversible pump turbine operating at deep partial load and under zero torque conditions. Two runner configurations, one with a 0° blades lean angle and the other with a -15° lean, were analyzed through transient simulations to assess their impact on pressure distribution, rotor-stator interactions, and frequency spectrum behavior. Results show that the runner with a -15° lean performs better, significantly reducing pressure fluctuations, torque perturbations, and radial force amplitudes. This improvement is particularly evident at higher harmonic frequencies (210 Hz), where the negatively leaned runner exhibits significantly lower susceptibility to rotor-stator interactions than the 0° lean configuration. This study enhances the understanding of the influence of runner geometry on hydrodynamic instability in reversible pump turbines, demonstrating that a negative lean configuration improves machine stability, reduces vibrations, and lowers acoustic emissions.