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In recent years, large-capacity, high-head pump–turbine units have been developed for pumped storage power plants to effectively utilise water energy and store large amounts of electricity. Compared with the traditional Francis turbine unit, the radial distance between the trailing edge of the guide vanes and the leading edge of runner blades of high-head pump–turbine unit is smaller, so the rotor–stator interaction and the corresponding pressure fluctuations in the vaneless space of pumped storage units are more intense. The pressure fluctuations with high amplitudes and high frequencies induced by rotor–stator interaction (RSI) become the main hydraulic excitation source for the structures of the unit and may cause violent vibration and fatigue damage to structural components, and seriously affect the safe operation of the units. In this paper, the RSI of a high-head pump–turbine in turbine mode of operation is studied in detail by means of site measurement and full three-dimensional unsteady simulations. The results of RSI-induced pressure fluctuations in turbine mode are analysed experimentally and numerically. The accuracy of the numerical calculations is verified by comparing with the measured results, and the variation law of RSI is deeply analysed. The results show that the pressure fluctuations in the vaneless space are affected by the wake of the guide vane, the rotating excitation of the runner, the low-frequency excitation of the draft tube, and the asymmetric characteristics of the incoming flow of the spiral case, and shows significant differences in spatial position. The findings of the investigation are an important and valuable reference for the design and safe operation of the pumped storage power station. It is recommended to design the runner with inclined inlets to reduce the amplitudes of RSI-induced pressure fluctuations and to avoid operating the pump–turbine units under partial load for long periods of time to reduce the risk of pressure fluctuation induced severe vibration on the structures.

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Reversible pump-turbine units of pumped storage power stations can generate power in turbine mode and store electric energy in pump mode for load balancing of the electric power grid. During the start-up transient process in pump mode of a reversible pump-turbine, the flow pattern and the pressure distribution in the flow channel change dramatically with the increasing opening angle of guide vanes. The unsteady pressure of the flow passing channel can cause severe vibration on the head-cover, bottom ring, and other stationary structures around the impeller. In this paper, a coupled 1D/3D co-simulation approach is developed to investigate the pressure distribution characteristics of the flow field during the start-up transient process in pump mode for a large prototype reversible pump-turbine unit. The entire model of flow channel from spiral casing to draft tube is constructed and the flow characteristics of key fluid fields such as spiral casing, stay vanes, guide vanes, impeller, and draft tube are analyzed. The simulation results show that under the condition of minimum guide vane opening the flow is insufficient and vortices occur on the impeller blades. The pressure distribution results of the flow channel from 3D fluid dynamic analysis during the start-up transient process in pump mode are exported as boundary conditions for the subsequent fluid-structure coupling analysis of the head-cover vibration investigation.