Analysis of the sound generated by the pairing of two axisymmetric co-rotating vortex-rings

The pairing of two axisymmetric co-rotating vortex rings is considered as a model problem for the interaction of the large scale structures in round jets. By using direct numerical simulations of the incompressible Navier-Stokes equations, the sound radiation of the interaction has been analyzed, with consideration of the effects of the Reynolds number and initial thickness of the rings. The acoustic signature of the interaction has revealed only minor effects of the Reynolds number. But the signature shows large effects of the vorticity distribution, with the eventual appearance of a secondary frequency.