Simulation of cavitation phenomena in Pelton turbine nozzle mechanisms under plateau conditions

Abstract This study employs numerical simulations to investigate the cavitation characteristics of the jet mechanism in a Pelton turbine operating in a plateau environment. The results indicate that as water flows through the converging section, its velocity increases sharply due to the reduced cross-sectional area, forming a highspeed jet at the nozzle outlet. The rapid flow causes a sudden drop in absolute pressure at the nozzle exit, reaching the saturation vapor pressure, which facilitates cavitation by allowing vapor nuclei to expand. It is observed that a “velocity deficit” occurs at the needle center due to flow obstruction, while a low-pressure region forms at the nozzle outlet due to high-speed jet ejection and air entrainment, both closely associated with cavitation. Additionally, the gaseous phase is primarily concentrated at the nozzle exit, with the cavitation region exhibiting an annular shape and a circumferentially uniform gas-phase volume fraction across all operating conditions. Based on the mass transfer rate model, simulation results, and experimental data, cavitation is found to be most pronounced at a nozzle opening of 40%.