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Numerical study of 2D stratified turbulence forced by internal gravity waves

Abstract : The oceanic motions are composed of eddies with a very large horizontal scaleand 3D propagating internal gravity waves. Its kinetic energy spectra follow thewell-known Garrett and Munk spectrum, which is usually interpreted as thesignature of interacting internal gravity waves. Our main motivation is toreproduce the turbulence regime observed in nature by forcing waves.Two-dimensional (2D) stratified flows on a vertical cross-section differ fromits analogous three-dimensional flows in its lack of vertical vorticity,supporting only waves and shear modes. In this PhD work, we perform a numericalstudy of 2D stratified turbulence forced with internal gravity waves. We get ridof the shear modes, sustaining a system only with wave modes. Unlike precedentstudies, the forcing is applied to a localized region of the spectral space, inwhich forced internal waves have a similar time scale. We forceintermediate-scale waves to allow the dynamics to develop both upscale anddownscale energy cascade.We first present the different regimes of 2D stratified turbulence with aparticular interest in the ocean-like regime, i.e. strong stratification andlarge Reynolds number. The dynamics of the energy cascade is analysed by meansof the spectral energy budget. Furthermore, we check if it is possible to obtainturbulence driven by weakly non-linear ineracting waves by performing aspatio-temporal analysis. To conclude, we report results of numericalsimulations forced either on the vorticity or on the eigenmode of theNavier-Stokes equations in order to study the degree of universality of 2Dstratified turbulence with respect to the forcing.
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Miguel Calpe Linares. Numerical study of 2D stratified turbulence forced by internal gravity waves. Mechanics of the fluids [physics.class-ph]. Université Grenoble Alpes [2020-..], 2020. English. ⟨NNT : 2020GRALI008⟩. ⟨tel-02612797v2⟩

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