On self-noise at the nose of a supercavitating vehicle

The cavity of a supercavitating vehicle in water is maintained by the steady injection of gas from sources within the vehicle and cavity. An analysis is made in this paper to estimate the spectrum of the acoustic 'self-noise' produced at the nose of the vehicle by the unsteady impingement of the gas on the cavity interface. For the purposes of calculation it is assumed that the supercavity is circular cylindrical and is formed to the rear of a hemispherical cavitator. This arrangement closely approximates a supercavity being investigated experimentally at the Penn State Applied Research Laboratory. A 'transfer function' is derived for this configuration that relates the self-noise pressure at the nose to the pressure distribution on the cavity wall attributable to the impinging gas. It is applicable also to any geometrically similar supercavity maintained by gas injection, provided that the distribution on the interface of the surface pressure spectrum of fluctuations produced by the impinging gas is known. Numerical results are given using experimental data for the cavity wall surface pressure produced by a narrow, impinging air jet and when the nose is acoustically hard, but the method is easily modified to deal with more general impedance conditions on the cavitator.