An axisymmetric hypersingular boundary integral formulation for simulating acoustic wave propagation in supercavitating flows

Abstract

Flow supercavitation begins when fluid is accelerated over a sharp edge, usually at the nose of an underwater vehicle, where a phase change occurs and causes a low density gaseous cavity to gradually envelop the whole object (supercavity) thereby allowing for higher speeds of underwater vehicles. The supercavity may be maintained through ventilated cavitation caused by injection of gases into the cavity, which causes fluctuations at the vapor-water interface. A major issue that concerns the efficient operation of an underwater object's guidance system (which is achieved by high frequency acoustic sensors mounted within the nose region), is the hydrodynamic noise produced due to the fluctuating vapor-water interface. It is important to carry out a detailed study on the effect of self-noise at the vehicle's nose that is generated by the ventilating gas jet impingement on the supercavity wall. For this purpose, the present study uses a boundary element method which is more versatile compared to other numerical techniques such as the finite element/finite difference methods. The variation of acoustic pressure at the vehicle nose for various shapes of cavitators, boundary conditions and jet impact diameters are presented. Comparisons are made with the semi-analytical procedure of Howe et al. (Howe et al., On self-noise at the nose of a supercavitating vehicle. Journal of Sound and Vibration, 322 (2009a), 772-784) and finite element based COMSOL commercial package. Several issues pertaining to the behaviour of analytical and numerical results are highlighted. Finally, the proposed boundary element technique is used to study arbitrary shapes of supercavities which may encountered at various stages of supercavity development. © 2012 Elsevier Ltd. All rights reserved.