Cavitation pressure fluctuation characteristics of a prototype pump-turbine analysed by using CFD

Abstract

Cavitation in water turbine can induce blade erosion, efficiency decrease and unit vibration, and in some extreme conditions the reverse water hammer caused by draft-tube cavity collapse may lead to the unit-lifting accident. The purpose of this work was to analyse the influences of cavitation on pressure pulsation characteristics of a prototype pump-turbine. We conducted 3D CFD simulations by giving different cavitation coefficients that induce different cavity volumes at the draft-tube inlet. In one of severe cavitation conditions, the propagation characteristics of cavitation pressures across the whole flow channel was studied, which was considered as the leading pulsating source. The correlation between pressure impulse and vapour fraction is successfully confirmed by observing the formation, development and collapse of the cavity in flow fields. The results indicate that the cavity, originating from the runner cone, evolves with various shapes, varying volumes and random periods, causing the wide spectrum band of frequencies of pressure pulsations. These results may lay the foundation for further studying extreme transient processes with cavity collapse.