Abstract
The present research clarifies the generating mechanism of the fluid vibration at emergency shutdown in a pump-turbine. The experiment and the numerical simulation for the pump-turbine were performed. The negative gradient of the pressure performance curve was observed in the experiment. The numerical result shows that the strong backflow and the second flow, observed at lower flow rates, cause the increase of the pressure loss in the blade passage, which leads to the negative gradient of the pressure performance curve. Furthermore, the angular momentum of the internal flow in the pump-turbine was examined. It was found that the region of the reverse pump in the blade passage exists in the turbine mode.
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