Experimental and numerical investigation of vortex flows and pressure fluctuations in a high-head pump-turbine

Vortex flows and pressure fluctuations, especially in the draft tube and vaneless space, have crucial impact on stable and safety operation for a high-head pump-turbine due to be fast adjusted and frequently switched between pump and turbine modes and often down to the deep part load. To more accurately investigate the vortex flows and pressure fluctuations in a high-head pump-turbine with splitter blades runner, a reliable approach by combined experiments with numerical simulations is presented in this paper. Laser Doppler Velocimetry measurements and high-speed camera observations inside the draft tube have been conducted at all the investigated points. Velocity profiles, vortex ropes visualization, the instantaneous tangential velocity and pressure fluctuations in both measured and simulated are presented to validate the numerical simulations and classify the vortex flow patterns. Meanwhile, the relationship between formation, development and breakdown of the vortex rope, the processional frequency and swirl intensity has been linked up and experimentally validated. Variation regularity of pressure fluctuations along the flow passage at different operating conditions has been quantitatively substantiated with measurements and predictions. Validation of predicted results versus experimental data shows that the presented numerical simulations can give very good results of vortex structures and the predicted fluctuation's frequencies. The pressure fluctuations amplitude of both the measured and the predicted in turbine mode agree well in the vortex rope-free zone, but has relatively larger deviations out of the vortex rope-free zone. It also demonstrated that the runner with splitter blades can restrain development of vortex flow and decrease the amplitude of pressure fluctuations for a high-head pump-turbine. The presented approach has been applied to successfully developed the high-head pump-turbines for several Pumped Storage Power Plants in China and demonstrated very useful in hydraulic optimizations.