Interactions onde-vortex en milieu stratifié tournant et transport à travers une barrière dynamique

Abstract : The interaction between inertia-gravity waves and vortices in a rotating stratified fluid is studied experimentally, and numerically using simulations based on the WKB theory also known as the ray theory. This study is carried out in the context of applications to geophysical flows. We consider the interaction of planar waves with cyclonic vortices: forced baroclinic vortices are generated by a small rotating disk whereas free rather barotropic vortices are generated by an elongated sink. In contrast to uni-directional flows, wave energy in axi-symmetric flows does not increase infinitely along critical surfaces. WKB simulations and experiments conjecture the existence of critical 'layers', of finite thickness, along which waves are trapped. WKB simulations capture the wave pattern observed in the experiments, and are used to predict the occurrence of wave breaking. We introduce an interaction Reynolds number for trapped waves, Rewave, which measures the ratio between the rate of decrease in wave-length and their viscous damping rate. For baroclinic vortices, the critical layers are inclined due to vertical shear and waves trapped along them do not break, due to low values of the Reynolds number. For barotropic vortices, the critical layers are almost vertical and most of the waves propagating against the flow are trapped, leading to wave breaking when the value of the Reynolds number is high enough, typically Rewave>200. This wave breaking is due to a local inversion of the density field, which drives a buoyancy-induced instability, and leads to the generation of negative vorticity in the outer region of the vortex. Mixing is driven by two distinct processes: vortex streamlines are destabilised by periodic wave disturbances and change into bands of chaotic mixing; wave breaking generates patches of turbulence of which the penetration into the vortex core depends on the amount of energy provided by breaking waves.
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Contributor : Frédéric Moulin <>
Submitted on : Wednesday, January 7, 2009 - 4:35:35 PM
Last modification on : Friday, October 11, 2019 - 8:22:31 PM
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Frédéric Moulin. Interactions onde-vortex en milieu stratifié tournant et transport à travers une barrière dynamique. Océan, Atmosphère. Université Joseph-Fourier - Grenoble I, 2002. Français. ⟨tel-00350836⟩

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