Ondes internes, de l'instabilité au mélange. Approche expérimentale

Abstract : Internal waves are believed to be of primary importance as they affect energy transfer, especially their dissipation mechanism. Therefore it is crucial to identify and measure the different processes evolving a transfer to smaller scales and leading to oceanic mixing. We have chosen to focus on one of these mechanisms: the Parametric Subharmonic Instability (PSI). This instability allows the generation from a primary wave of two secondary internal waves, with different frequencies and waves vectors, by nonlinear resonant interaction. The experimental study of this instability has helped to highlight the importance of some parameters (frequency, amplitude, beam width) for the development and the selection of secondary waves. Thus these parameters affect the energy transfer between scales. Moreover, our experimental device was used to test the limits of the theory developed so far and has led to the development of a new model, which has been validated experimentally and numerically.In addition, we adapted the technique of Laser Induced Fluorescence (LIF) to continuously stratified fluids, with the aim of performing simultaneous measurements of velocity (PIV) and density (LIF). This technique allows us to study experimentally the effect of propagation and destabilization of internal gravity waves on a linear stratification, and to access to quantities related to the mixing.
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Baptiste Bourget. Ondes internes, de l'instabilité au mélange. Approche expérimentale. Physique Générale [physics.gen-ph]. Ecole normale supérieure de lyon - ENS LYON, 2014. Français. ⟨NNT : 2014ENSL0912⟩. ⟨tel-01073663⟩

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