Sound Generated by Gas-Jet Impingement on the Interface of a Supercavity

Predictions are made of the sound produced by the impingement of ventilating air jets on the gas-water interface of a ventilated supercavity. The interface is rippled by the jets, and the unsteady surface forces exerted on the water constitute acoustic sources of dipole type. Typical gas speeds on impact do not normally exceed about 60 m/s. In these circumstances the very large difference in the densities of the gas and water imply that the dynamics of the jet-wall interaction are, in a first approximation, similar to those occurring when a jet impinges on a rigid wall. An independent, canonical experiment is performed to determine the frequency spectrum of the surface force distribution produced by a single turbulent jet impinging on a wall, for several different injection flow rates and jet lengths, and thence to estimate the sound produced in the water when the same jet impinges on the cavity interface. The result is used to predict the contribution produced by this mechanism to the overall water borne noise generated by a specially constructed supercavitating body used at the Applied Research Laboratory at Penn State University, for which the ventilating gas enters the cavity axisymmetrically through a series of radially orientated nozzles equally spaced around a gas injector ring. A comparison is made with predictions based on force measurements of Strong, et al. [1].