NONLINEAR SOUND-VORTEX INTERACTIONS IN AN INVISCID ISENTROPIC FLUID -A 2-FLUID MODEL

A new two-fluid model is developed to describe the nonlinear interacti on of acoustic waves and vortices. Analytical and computational result s are presented for a sound pulse interacting with and being modified by a vortex. A novel numerical method based on a particle-in-cell disc retization of the acoustic field is developed and used to study the no nlinear scattering of sound by a cylindrical vortex. Equations for the sound wave packet propagating in an axially symmetric mean flow are i ntegrated analytically. Nonlinear modification of the vortex flow by t he high-frequency sound is found to be mediated by growing pressure di sturbances generated by the radiative forcing on the high gradient reg ions of the acoustic pulse. The total energy of the vortex mean flow g rows monotonically, as the acoustic component loses its energy. The ch anges in the kinetic and internal energies of the vortex are greater t han the changes in its total energy, although these changes are revers ible in lowest order of the nonlinear vortex-acoustic interaction. (C) 1995 American Institute of Physics.