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SUMMARY:Stirring vortices with vorticity holes - Velasco Fuentes\, O (CICE
 SE\, Mexico)
DTSTART:20120726T091000Z
DTEND:20120726T093000Z
UID:TALK39070@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:A vorticity hole is a region with\, in absolute value\, signif
 icantly lower vorticity than its surroundings. Here we discuss the dynamic
 s of a Rankine vortex with either one elliptic hole or two equal circular 
 holes. If we assume symmetry and null vorticity within the holes\, the evo
 lution only depends on the hole size and either the aspect ratio of the el
 liptic hole or the separation of the circular holes. We computed the evolu
 tion with a contour-dynamics model and found that it is analogous to eithe
 r that of the Kirchhoff vortex or that of the vortex pair\, but the vortic
 ity holes are additionally affected by their interaction with the boundary
  of the Rankine vortex. To quantify the stirring of fluid particles\, both
  inside and outside the vortex\, we analysed the set of hyperbolic traject
 ories and associated manifolds of the time-evolving velocity field. The st
 rongest stirring always occurred in the areas of highest vorticity\, which
  contradicts the generally accepted notion that vortices are regions of nu
 ll to weak stirring.\n\n
LOCATION:Seminar Room 1\, Newton Institute
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