An Experimental Study of Single Bubble Cavitation Noise

Abstract

An experimental study of single bubble cavitation noise has been made. Single bubbles were produced either by a venturi nozzle or by a spark technique. The motion of the bubbles was studied photographically and simultaneously the noise measured. The noise consists principally of a shock wave associated with the collapse of the bubble. There are other sources of noise but they are of minor importance. The pressure versus time records permit the spectrum to be easily computed by Fourier transforms. Rayleigh treated the motion of an empty spherical bubble in an incompressible fluid. He showed that when the bubble collapses the radial velocity becomes infinite and an infinite pressure is developed. Incompressibility is clearly an untenable assumption. Also, the thermodynamics of the bubble contents must be considered. It was observed experimentally that the air content of the bubbles is the dominant factor in determining the magnitude of the pressure shock wave. When the air content becomes small compressibility becomes the dominant factor in determining the magnitude of the pressure shock wave. The venturi bubbles and the spark bubbles behave differently as might be expected since the thermodynamics of their contents are different.