Abstract
The sound production by vortex rings is investigated by means of an
axisymmetric vortex particle method. The predictions are first calibrated
by analyzing the noise generated by steady vortex rings that are described
by the analytical solutions of Fraenkel and Norbury. The noise produced by
isolated vortex rings for both nominally steady and unsteady cores is then
analyzed. For nominally steady cores, computed results indicate that the
efficiency of sound radiation decreases as the slenderness parameter is
reduced, and the acoustic signals reveal a dominant period that is
approximately half the eddy turnover time. For unsteady cores, the
amplitude of the radiated sound is substantially higher than that of
similar steady rings. When the initial core vorticity distribution is
nonuniform, complex internal motion may also occur within the core
which is also reflected in the corresponding far-field acoustic signal.
Finally, the effect of vortex stretching is analyzed based on computations
of two coaxial corotating vortex rings.