Abstract: The runaway transient process after pump-trip accompanied by invalid wicket gates is an event very dangerous to pumped-storage power stations. Violent fluctuations in water hammer, flow patterns, pressure pulsations, and runner forces are the issues that lack understanding and need further studies. In this work, A CFD method coupling the one-dimensional waterway flow and three-dimensional flow was adopted in a model pump-turbine to simulate this fast-evolving process. Analyzing the histories of discharge, rotational speed, and runner forces, it find that the fluctuations of these parameters are obvious in the hump and S regions of the characteristic curves. Examining pressure pulsations at different monitoring points, it find that the pulsating characteristics all over the four-quadrant characteristic plane are complicated and can be classified to four types: high frequency-low amplitude, high frequency-high amplitude, middle frequency-middle amplitude, and low frequency-high amplitude. In the hump and S regions, both high- and low-frequency components become stronger, while in the normal operation regions all the components calm down. The flow patterns shows that high-frequency components come from rotor-stator interaction, and middle- and low-frequency components are from the vortices in the sections of guide vanes, runner blades and draft tube.

Key words: pump-turbine, pump-trip runaway process, hydraulic transient, pressure pulsations, draft-tube vortices