Abstract: Vibrations of pump-turbine units are often severe during load rejection, and the resulted intensive alternating stress may lead to a fatigue failure of the runner. To investigate the flow-induced vibrations of a pump-turbine runner, flow patterns, dynamic stress, and vibration modes are analyzed for typical working conditions based on CFD-FEM simulations. The results show the rotational speed is the key factor that has the greatest influence on the pressure pulsation and dynamic stress of the runner. Working at the highest speed is the most adverse condition, resulting in the worst pressure pulsation, along with a dynamic stress and its fluctuating amplitude that both are larger than those in other working conditions. The fluctuation of runner stress is induced by pressure pulsation, both featured with similar frequency spectra. The peak dynamic stress of the runner is located at its T-shaped joint between the blade leading edge and the hub. In our calculations, the frequencies of hydraulic excitation forces are far away from the natural frequency of the runner, and therefore the runner will not resonate in this case.

Key words: hydraulic machinery, pump-turbine, load rejection, flow-induced vibration, fluid-structure interaction, CFD-FEM