Spectrum of the sound produced by a jet impinging on the gas-water interface of a supercavity

An analysis is made of the sound generated by the impingement of an air jet on the gas-water interface of a supercavity. The water is in uniform low Mach number motion over the interface. The interface is rippled by the jet, which produces an unsteady surface force on the water that behaves as a dipole or monopole acoustic source, respectively, at high and low frequencies. In a first approximation the very large difference in the gas density and that of water implies that the surface force is similar to that occurring when a jet impinges on a rigid wall. Data from recent measurements by Foley (2009, Ph.D. Dissertation, Department of Mechanical Engineering, Boston University) of the frequency spectrum of the surface force produced by the impact of a turbulent jet on a wall are used to formulate an analytical representation of the spectrum and thence to predict the sound produced in water when the same jet impinges on the cavity interface. The prediction is used to estimate the characteristics of gas jet impingement noise for an experimental supercavitating vehicle in use at the Applied Research Laboratory of Penn State University.