Experimental studies of unsteady cavitation at the tongue of a pump-turbine in pump mode

The paper deals with the cavitation at tongue of a pump-turbine in pump mode, including the typical patterns, unsteady behaviors, and the influence on pump performance and fluid-borne noise. Visuali-zation experiments were conducted under different flow rates and rotational speeds for variation cavity regimes. The results show the patterns can be divided into three regimes with cavitation development: bubble cavitation, cloud cavitation, and lock cavitation for the gas-lock phenomenon and performance plummet. The rotor-stator interaction and jet-wake flow could affect the cavitation generation. The blade passing effect is the leading cause of bubble clusters periodic collapsing or shedding at the early stages of cavitation, while playing a small role as cavities become thick and evaporation rate rises. The combined action of the attached vortex (re-entrant jet) and the depression by pressure gradient outside cavity surface account for the shedding at the developed cloud cavitation stage. Based on the noise measure-ment by hydrophone at the outlet, the broadband sound in the range of 1000 HZ-200 0 Hz can be used for cavitation detection since it can be rarely influenced by operating conditions under non-cavitation. (c) 2021 Elsevier Ltd. All rights reserved.