The influence of nucleation on cloud cavitation about a sphere

The influence of nucleation on cloud cavitation about a sphere is investigated using simultaneous high-speed photography and high-frequency surface pressure measurements. The 0.15 m diameter PVC sphere was located on the axial centreline of a variable-pressure water tunnel with a 0.6 m square test section and tested at a constant Reynolds number of 1.5×10⁶ and a cavitation number of 0.7. The flush-mounted high-frequency pressure sensor was located within the shedding zone of the cloud cavitation and orientated such that it was in the field of view of the high-speed camera. Pressure measurements and high-speed photography were simultaneously obtained at 7 kHz. The time-series of spatially averaged image pixel-intensity was found to lead the pressure measurement. Wavelet analysis was used to compare both data sets obtained for cavitation about the sphere with and without upstream artificial nuclei seeding. PSDs generated from the wavelet analysis showed two peak frequencies for the cavity shedding, with the peaks being more defined for the nucleated case.