On sound radiated from a perturbed vortex ring

An analysis of the evolution and sound radiation of a slender vortex ring with initial weak perturbation in free space has been done. Depending on the integer wavenumber of perturbation, the circulation and the core size of the vortex ring, the perturbation evolves in either stable or unstable modes. Both stable and unstable evolutions radiate sound in the far field, and the vortex acceleration of the vortex has been found to be a major sound radation mechanism. A stably perturbed vortex ring radiates stronger sound than an unstable one. The finding of the present study explains some experimental observations of sound from an isolated vortex ring.