Abstract：In order to investigate the pressure fluctuation characteristics of pump-turbine in turbine mode, a three-dimensional unsteady flow in a pump-turbine is numerically simulated using the shear stress transport(SST)k-ω turbulence model. By comparing computational flow discharge and efficiency with experimental ones, the flow models are validated. The pressure fluctuations in the guide vanes, runner and draft tube under three different operational conditions are analyzed, respectively. The results show that both the shape and the rotating direction of vortex rope have an obvious influence on the pressure fluctuation. At a low discharge, vortex rope is helical and has the same rotating direction with the runner, a severe low-frequency pressure fluctuation appears at the runner outlet. The frequency of pressure fluctuation on the runner blade is about 0.62 times the runner rotational frequency and the dominant frequency in the draft tube is about 0.36 times the runner rotational frequency. At an optimum and large discharge, the vortex rope is tubular, the amplitude of pressure fluctuation at the runner outlet is reduced. The dominant frequency of the pressure fluctuation in the draft tube is the same as the frequency of pressure fluctuation on the runner blade. At a large discharge, the vortex rope is in the inverse rotating direction of the runner, and the maximal amplitude in the pressure fluctuation in the draft tube appears at the tube elbow.
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