To study the inner flow mechanism of pump turbine in the braking operation with vanes′ abnormal vibration, the numerical simulation was done with the SST k-ω turbulent model and SIMPLEC algorithm. The analyses of vane region′s flow and pressure fluctuation were done after comparing with the data from experiment which was finished before. The results show that there exists wake structure after the guide vanes and stay vanes. There will be a loss of energy in the transformation between them and it could cause hydraulic vibration. There also exists impact loss in the inlet of guide vanes which increases the instability of guide vanes region. The instability of the flow in the guide vanes is further verified by the pressure fluctuation monitoring in the guide vanes region. Through the analyses of time domain and frequency domain characteristics, they show that the relative amplitude has reached more than 3 times of normal working conditions of turbine mode and pump mode. The main frequency is theblade frequency with high amplitude. It is an intermediate frequency component which could cause resonance. The results can be used to guide the optimal design of the pump turbine.
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