Elastic Interaction between a Vortex Dipole and an Axisymmetrical Vortex
in Two-Dimensional Flows
Abstract
We investigate numerically the elastic interaction between a dipole and
an axisymmetrical vortex in inviscid isochoric two-dimensional flows
satisfying Euler’s vorticity conservation equation. This work
contributes to previous studies addressing inelastic vortex
interactions. The dipole is a straight moving Lamb-Chaplygin (L-C)
vortex, where the absolute value of either the positive or the negative
amount of vorticity equals the amount of vorticity of the target vortex.
The results show that, when the straight moving L-C dipole approaches
the axisymmetrical vortex, the potential flows of both vortices
interact, the dipole’s trajectory acquires curvature and the dipole’s
vorticity poles separate. Once the L-C dipole moves away from the target
vortex, the poles close and the dipole continues with a straight
trajectory but along a direction different from the initial one. Though
there is very small vorticity exchange between the dipole’s poles and a
small vorticity leakage to the background field, the vortices preserve,
to a large extent, their amount of vorticity and the resulting
interaction may be practically qualified as an elastic interaction. This
process is sensitive to the initial conditions and, depending on the
initial position of the dipole as well as on small changes in the
vorticity distribution of the axisymmetrical vortex, inelastic
interactions may instead occur. Since the initial vorticity
distributions are based on the eigenfunctions of the two-dimensional
Laplacian operator in circular geometry these results are directly
applicable to three-dimensional baroclinic geophysical flows under the
quasi-geostrophic approximation.