In order to study the fluid flow and pressure fluctuation characteristics in the turbine mode of a pump-turbine, the geometrical model of a pump-turbine in a pumped storage power station is generated, and unsteady three-dimensional flows in the turbine mode are simulated by employing the RNG k-ε model and SIMPLE algorithm under 25%, 50%, 75% and 100%(full)load conditions, respectively. At the same time, the pressure pulsations at the inlet of volute, in the range of wicket gate, in the vaneless range between the wicket gate and the runner, in the conical diffuser and elbow of the draft tube are monitored. The results show that jet flows are issued at the wicket gate outlet under no-load and 25% load conditions, causing a deteriorated flow field in the vaneless range and a vortex structure near the runner inlet, fortunately this situation is relieved with increasing load. Under 50 % load condition, there are a few vortex rope branches to intertwine each other, the vaneless range is affected by the rotor-stator interaction of high frequency, and the flow in the draft tube is influenced by vortex ropes of low frequency, further, the interaction and rope low frequency pulsation propagate upstream and downstream, respectively. Under 75% and full load conditions, the pressure fluctuation amplitude decreases from monitoring points P1 to P5, particularly, the amplitude at point P3 in the vaneless range and point P4 in the conical diffuser declines sharply. The pulsation frequency in the vaneless range remains unchanged when the load changes, and the amplitude of various frequencies rises with increasing load.
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