The roles of shock motion and deformation in generation of shock noise

Abstract

This paper investigates two mechanisms fundamental to sound generation in shocked flows: shock motion and shock deformation. Shock motion is modeled numerically by the interaction of a sound wave with a shock. The numerical approach is validated by comparison with results obtained by linear theory for a small disturbance case. Analysis of the perturbation energy using Myers' energy corollary demonstrates that both acoustic and entropy energies are generated by the interaction of acoustic disturbances with shocks, and suggests that shock motion is the source of the disturbance energy. Shock deformation is modeled numerically by the interaction of a vortex ring with a shock. The numerical simulations demonstrate the generation of both an acoustic wave and contact surfaces. The acoustic wave spreads cylindrically, the sound intensity is highly directional, and the sound pressure increases with increasing shock strength. The numerically determined relationship between the sound pressure and Mach number is found to be consistent with experimental observations of shock noise, and implies that a dominant physical process in the generation of shock-noise is modeled in this study.