Exploratory Experiments to Determine Flow and Structure Borne Noise of Erosive Cavity Implosions

In two exploratory setups, a high-frequency pressure transducer has been used to determine both the flow and the structure borne noise above 200 kHz. In the first set of tests the impact noise due to a single bubble is investigated in order to gain insight in the acoustic signals emitted by an imploding bubble. A quantitative analysis of the signals indicates a short and clear acoustic signal in the fluid and a long chiming signal in the structure. In the second set of tests the noise signal emitted by sheet cavitation implosion on a hydrofoil is acquired. The convoluted signals of individual bubbles can be identified both in the fluid and in the structure. Analyses of the signals by examining the peak distribution for sheet cavitation indicates a relation with the cavitation index and suggest that fluid and structure borne noise are not per se linked. Acoustic signals correlate well with visual observation.