Abstract: A pump turbine often experiences vibrations and abnormal noises from its distributor during pump mode shutdown from a guide vane opening less than the maximum opening of 20%. To eliminate this instability, we carry out numerical simulations of the transient flow in guide vane section, investigate variations in flow pattern during shutdown, and verify the necessity of power cutoff in advance. Two-dimensional periodic simulations are adopted to consider periodicity in the flow and guide vane movement during shutdown, and a dynamic meshing technique is used to discretize the guide vane domain with a finite volume method and a RNG k-ε two-equation turbulence model. The boundary conditions of 2D modeling are specified using the results of transient calculation for the hydropower station. The results indicate that during a pump mode shutdown, the scheme of power cutoff in advance at an appropriate opening improves the stability of guide vane flow, thereby lowering the probability of generating vibrations and abnormal noises. Further analysis shows that the flow stability of guide vane channels is positively correlated with the opening threshold for power cutoff. And we suggest an opening threshold in the range of 3-6 degrees for practical operation of hydropower plants.

Key words: pump turbine, shutdown process, pump mode, power cutoff in advance, slight opening zone, unstable flow, vibration and abnormal noises