Abstract: The ultra-high head pumped storage unit connects to a long water pipeline system. In its transient process, pressure pulsation and flow evolution are more complicated, and the hydraulic instability often occurs in the unit. Based on the one-and-three-dimensional model-coupling method and the dynamic mesh technology, this paper conducted numerical simulation on the pump power-trip process of an ultra-high head pumped storage unit. We examine the transient characteristics and high amplitude pressure pulsation by combining time-frequency analysis and internal flow field analysis, focusing on the instability development mechanism. Apart from the high frequency pressure pulsation caused by the rotor-stator interference during the pump power-trip process, this study shows that in the stay vane area, the low-frequency pressure pulsations occurred are induced by the rapid movement of the vortices and local backflows at the high-pressure inlet of the runner. While in the guide vane area, the high amplitude pulsations are caused by the flow collision. The results are meaningful for the hydraulic design and operation of ultra-high head pumped storage units.

Key words: ultra-high head pumped storage unit, pump power-trip, transient process, pressure fluctuation, internal flow field