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SUMMARY:Instabilities of a columnar vortex in a stratified fluid - Meunier
 \, P (CNRS)
DTSTART:20081208T140000Z
DTEND:20081208T143000Z
UID:TALK15636@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:The stability of a columnar vortex in a stratified fluid is ad
 dressed theoretically and experimentally.\n\nIn a first part\, we show tha
 t the addition of a small tilt angle between the vortex axis and the densi
 ty gradient direction changes drastically the structure and stability of t
 he vortex. For Froude numbers larger than one\, a strong axial flow is cre
 ated around the critical radius where the angular velocity equals the Brun
 t-Vaisala frequency. For large Reynolds numbers\, this axial flow is suffi
 ciently localized in the critical layer to become unstable with respect to
  the shear instability. Theoretical predictions for the structure of the c
 ritical layer and the instability characteristics are compared with experi
 mental results.\n\nIn a second part\, we analyse the stability of a vortex
  aligned along with the density gradient direction. We show that the linea
 r modes of the vortex are weakly unstable for small Froude numbers. These 
 modes are radiative at large radii\, which means that the vortex generates
  internal waves spontaneously. At moderate Froude numbers\, these radiativ
 e modes cease to be unstable. However\, a resonance between the radiative 
 modes and the Kelvin modes of the vortex becomes possible leading to insta
 bility in narrow wavenumber bands. 
LOCATION:Seminar Room 1\, Newton Institute
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