Abstract
This study performs numerical simulations to investigate the hydraulic torque characteristics of a pump turbine at different guide vane openings in pump mode. The SST k-ω turbulence model is utilized to simulate the flow field at guide vane angles from 1° to 21°. The simulation results reveal that the overall hydraulic torque shows a decreasing trend as guide vane opening increases. However, significant asymmetry of hydraulic torque exists among different guide vanes at certain openings. This asymmetry highly correlates with the large vibration observed during pump start-up in the field test. By analysing pressure contours and velocity streamlines at openings of 3°, 9° and 17°, the causes for torque asymmetry are explored in depth. The primary factors are identified as circumferential flow non-uniformity, distinct flow discharge tendencies between boundary guide vanes, and reverse flow towards upstream stay vanes. The research findings provide important insights into the hydraulic torque characteristics of pump turbines at off-design conditions, and offer valuable guidance for the optimal design and stable operation of pump turbines in pump mode.
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