Nonlinear Wind-up in a Strained Planar Vortex
Charles Macaskill, Andrew P. Bassom and Andrew G. Gilbert
Research Report 2000-15
Date: 8 June 2000
The response of a Gaussian vortex to a strong external strain field is
examined using two complementary numerical schemes. When the strain is
weak previous calculations have shown that a rebound phenomenon is
operative: after enstrophy is transferred from the mean to the
azimuthal component by the straining there is a reversal during which
a significant fraction of the enstrophy moves back from the
azimuthal component to the mean.
Concomitantly the perturbation vorticity undergoes spiral wind-up and
develops a short-scale radial structure which becomes ever finer with time.
We show that the rebound behaviour is suppressed by strong strain and that the
intricate radial structure is simultaneously inhibited. We also give some
indication of the modifications that are introduced when a strongly strained
vortex is allowed to relax after the forcing field is switched off.
vortex dynamics. pseudo-spectral techniques. contour dynamics.
AMS Subject Classification (1991)
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Sydney Mathematics and Statistics