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Accueil > Grands équipements > La plateforme tournante Coriolis > Projets de recherche > Archives 2005

The structure and dynamics of dipolar vortices in a stratified fluid

Praud O., Fincham A.,J. Fluid Mech. 544, 1-22 (2005)

The three-dimensional structure and decay of a dipolar vortex in a linearly stratified
fluid is investigated experimentally using a high-resolution three-dimensional scanning
correlation image velocimetry system (SCIV). Comparisons with simple theoretical
and numerical models are made for late times in the low-Froude-number regime.
The relatively well-known stratified dipole, most of the time assumed to be quasitwo-
dimensional, is revealed to have a complex three-dimensional vortex topology
arising from its self-induced propagation. As the buoyancy scale u/N approaches
zero the dynamics of such a structure are dominated by the horizontal velocity field,
whereas the diffusion is mainly vertical. The evolution is then governed by an effective
Reynolds number, Reeff, based on vertical diffusion and horizontal advection. At early
times this effective Reynolds number is large, horizontal advection terms dominate
and a decrease of aspect ratio of the structure is observed until Reeff reaches a
critical value Rec
eff \u223cO(1), independent of the initial condition and associated with
a horizontal advection\u2013vertical diffusion balance. Thereafter the evolution becomes
purely diffusive with decay time Rec