Study on suppression of cavitating vortex rope on pump-turbines by J-groove

Pumped hydro energy storage systems are a reliable solution for maintaining grid stability. However, the pump turbines utilized in these systems often display instability due to pressure fluctuations, and the draft tube experiences additional fluctuations from the formation of a cavitation and vortex rope. This paper introduces a novel J-groove design method and presents four different designs of J-grooves. Unsteady analysis is performed.The J-grooves reduce the magnitude and alter the distribution of axial and tangential velocities inside the draft tube, which results in the disruption of vortex rope through the generation of jet flow from J-grooves. The grooves exhibit noticeable suppression effects on cavitation, vortex rope and pressure fluctuations, while this comes at the expense of efficiency. J-grooves with uniform thickness significantly suppress pressure fluctuations, while thickening the leading and rear edges respectively benefits the suppression of runner and draft tube cavitation. The cavitation suppression effectiveness of the long-short type J-groove is inferior to the other models, but it incurs lower efficiency losses. These findings provide insights into the suppression of cavitation and vortex rope and are of significant importance for the optimization of J-grooves.