DYNAMICS OF A VORTEX RING IN A ROTATING FLUID

The formation and the evolution of axisymmetric vortex rings in a unif ormly rotating fluid, with the rotation axis orthogonal to the ring vo rticity, have been investigated by numerical and laboratory experiment s. The flow dynamics turned out to be strongly affected by the presenc e of the rotation. In particular, as the background rotation increases , the translation velocity of the ring decreases, a structure with opp osite circulation forms ahead of the ring and an intense axial vortex is generated on the axis of symmetry in the tail of the ring. The occu rrence of these structures has been explained by the presence of a sel f-induced swirl flow and by inspection of the extra terms in the Navie r-Stokes equations due to rotation. Although in the present case the s wirl was generated by the vortex ring itself, these results are in agr eement with those of Virk et al. (1994) for polarized vortex rings, in which the swirl flow was initially assigned as a 'degree of polarizat ion'. If the rotation rate is further increased beyond a certain value , the flow starts to be dominated by Coriolis forces. In this flow reg ime, the impulse imparted to the fluid no longer generates a vortex ri ng, but rather it excites inertial waves allowing the flow to radiate energy. Evidence of this phenomenon is shown. Finally, some three-dime nsional numerical results are discussed in order to justify some asymm etries observed in flow visualizations.