Noise from pulsating super cavities and its control

The noise radiated by pulsating supercavities has been measured in a water tunnel facility. The noise was found to be single frequency and monopole in nature with a spectrum level given by the level of the cavity interior pressure and attenuation due to spherical spreading from the interface. The radiated noise levels from pulsating supercavities were found to be at least 35 dB higher than those radiated by comparable re-entrant jet and twin vortex supercavities. Initial investigations were performed into suppressing pulsation noise by modulating (i.e., adding a sinusoidal component to) the gas ventilation rate in order to shift the supercavity resonance frequency away from the interface excitation frequency. This technique, which has its roots in parametric oscillators, caused pulsating supercavities to transition to another (twin vortex) closure regime over a certain range of modulation frequencies. Other ventilation gas modulation frequencies caused the supercavity pulsation and resonance frequency to increase over its steady (no-modulation) ventilation flow rate frequency but pulsation persisted and the radiated noise levels remained largely unchanged.