Acoustic instability of vortices

Abstract

Large plane is a powerful source of vortex. Disturbances of an axial vortex in a compressible fluid are unstable with respect to Kelvin wave development and produce acoustic wave generation. On the other hand system of counter-rotating vortices (Lamb dipole), with different intensity of vortices, as a result of instability collapse into the center of rotation of vortices. The characteristic time of collapse is in the reciprocal proportion the vortices intensity difference. The evolution of Lamb dipole, determined by the two competing processes of instability, is considered in the presented paper. The sound radiation of Lamb dipole can be used to estimate the vortex structure produced by large plane. The advent of large aircraft, with their attendant large and strong trailing vortex structures, made this a problem of considerable practical concern.