Free gas content effects on cavitation inception and noise in a free shear flow

Cavitation inception and the resulting acoustic signature from cavitation in the wake of a sharp edged disk have been studied experimentally in a large water tunnel. The investigation was carried out with four disks ranging in size from 2 to 16cm over a Reynolds number range of about 8x104 to 2x106. The spectrum of noise measured with a hydrophone is correlated with measurements of the number and size distribution of upstream nuclei measured with a laser scattering technique. A strong relationship between the acoustic signature and the nuclei content is noted. Especially prominent is a sharp shift in spectral energy content from high to low frequencies when the liquid is supersaturated under test section pressure. It is also found that the intensity of pressure fluctuations in the wake, which induce the cavitation, are strongly related to the boundary layer characteristics on the face of the disk