Spectral Content of Cloud Cavitation about a Sphere

Cloud cavitation about a sphere is investigated in a variable-pressure water tunnel using simultaneous high-speed photogra-phy and high-frequency surface pressure measurements. The 0.15 m diameter PVC sphere was located on the axial centre-line of the 0.6 m square test section and tested at a constant Reynolds number of 1.5×106 and cavitation numbers ranging from 0.4 to 1.0. The flush-mounted high-frequency pressure sensor was located within the shedding zone of the cloud cavi-tation and orientated such that it was visible by the high-speed camera. Pressure measurements were recorded at 7 kHz. The high-speed photography was simultaneously obtained at 7 kHz and a time-series of the pixel-intensity was extracted at the pres-sure sensor location. The spectral content of the cloud cavita-tion was obtained from frequency analysis of the time series from the surface pressure measurements and high-speed pho-tography. The coherence of the two signals was measured using Pearson’s Correlation Coefficient, for which the values ranged between 0.57 and 0.73. Both data sets were investigated using wavelet analysis. Two peak frequencies are observable at most cavitation numbers tested that correspond to different shedding modes relating to cavity length