On noise emission during coaxial vortex ring collision

Vortex simulations of coaxial vortex ring collisions are used to predict the impact of 3D vortex motion on far-field noise radiation. It is shown that nonlinear growth of azimuthal bending waves on rings with moderate core size to radius ratio leads to small departures from axisymmetric predictions. Meanwhile, the evolution of traveling waves on slender vortices results in large increase in acoustic pressure levels. It is suggested that the observed differences are linked to small nonlinear time-scales which characterize slender cores, and to convolutions in pressure predictions which naturally minimize the impact of high wavenumber modes.