Vortex and energy characteristics in the hump region of pump-turbines based on the rigid vorticity and local hydraulic loss method

With the climate change hazards and implementation of pumped-storage hydropower units in the power grid increases, maintaining hydraulic stability in the hump region is primordial for the energy transition yet presents a significant challenge. This study investigates the energy loss characteristics and hydraulic instability of the pump-turbine during operation in the hump region using both model testing and computational fluid dynamics methods. The results indicate that the energy loss predominantly occurs in the guide vane (GV) passage and draft tube (DT), more with flow reduction. Specifically, energy loss in the vaneless space is linked to shear vorticity, while rigid vorticity plays a prominent role in the GV passage and DT. Analysis using the Rortex enstrophy transport equation shows that the pseudo-Lamb term is the dominant factor influencing vortex evolution. Additionally, combining Reynolds-averaged Navier–Stokes equations with particle image velocimetry experiments reveals significant rigid vorticity near the zero-velocity gradient region, while shear effects are concentrated in the vortex core region on the runner side, primarily in the wake direction of vortex motion.