Effect of Vortex Profile on Sound Generation in a Non-uniform Flow

Abstract

The propagation of acoustic waves originating from stretching of intense self-similar vortices in the non-uniform mean flow is studied by numerical modeling using high-order compact approximation

Near-wall stretching of initial vortex by the stagnation flow leads to sound radiation from the generated pressure quadrupole. To mimic unsteady stagnation flows and impingement jets, the stagnation flow has been switched off at some time moment. Subsonic stagnation flow and flow around a cylinder are taken as prototypes of real-world flows with strong gradients of mean pressure and velocity. Compressibility of the background mean flow and the vortex are taken into account and its effect on amplification of acoustic pressure is discussed. Generation of sound by stretching of vorticity dipole leads to formation of a three-spot wave with maximum acoustic pressure at the centerline. Since aeroacoustic applications require good physical approximations for the viscous nature of tip vortices, several semi-empirical profiles of vortex velocity were considered. The intensity and directivity of acoustic wave patterns appear to be quite different for Taylor and Vatistas vortices.