Noise generation in cavitating flows

Measurements of the pressure fluctuations in the near field of a submerged jet are reported. The mechanisms by which the pressure fluctuations are generated are discussed, and the transient oscillations of microbubbles of air excited by the pressure drop in the nozzle, and the cavitation of microbubbles by the turbulent pressure fluctuations in the jet mixing region are estimated. The power spectral density of pressure fluctuations shows a broad flat peak at higher frequencies, rising steadily with velocity. When a critical cavitation number is reached the noise radiated from the collapse of the cavitation bubbles in the mixing region is detected and inception is defined. Below inception this noise component shows a sharp peak which first rises very rapidly and then in proportion to the cavitation number.