Dynamics and Noise Emission of Laser Induced Bubbles in a Vortical Flow Field

Abstract

The sound produced by the collapse of discreet cavitation bubbles was examined. Laser-generated cavitation bubbles were produced in both a quiescent and a vortical flow. The sound produced by the collapse of the cavitation bubbles was recorded, and its spectral content was determined. It was found that the rise time of the sound pulse produced by the collapse of single, spherical cavitation bubbles in quiescent fluid exceeded that of the slew-rate of the hydrophone, which is consistent with previously published results. It was found that, as the collapsing bubbles were deformed by the vortical flow, the acoustic impulse of the bubbles was reduced. Collapsing non-spherical bubbles often created a sound pulse with a rise time that exceeded that of the hydrophone slew-rate, although the acoustic impulse created by the bubbles was influenced largely by the degree to which the bubbles became non-spherical before collapse. The noise produced by the growth of cavitation bubbles in the vortex core was not measurable. These results have implications for the interpretation of hydrodynamic cavitation noise.