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Études expérimentales d'ondes d'inertie en régime non-linéaire : attracteurs et turbulence d'ondes

Abstract : Fluids submitted to a global rotation, through the action of the Coriolis force, allow the propagation of internal waves called inertial waves which are one of the key ingredients of geophysical and astrophysical flow dynamics. This thesis provides elements of understanding about the question of the role of inertial waves in turbulent flows subject to a global rotation. We present two experimental studies of flows with the originality of being forced only through inertial waves. In the first one, we study a wave mode called wave attractor in which all the energy at a given frequency tends to concentrate on a limit cycle. We point out that the attractor is subject to a triadic resonance instability which has the consequence of reducing the relative amplitude and increasing the wavelength of the attractor. We show that this non-linear regime of the attractor can be described quantitatively by replacing in the linear model the viscosity of the fluid by a turbulent viscosity, taking effectively into account the dissipation that the instability creates for the attractor. The second study focuses on a flow forced by an assembly of numerous inertial wave beams propagating in different directions. For a moderate amplitude of the forcing, the forced waves are subjected to a triadic resonance instability. Stronger forcing however does not lead to an inertial-wave turbulence regime. Instead, we show that the majority of the energy goes in a geostrophic mode. We propose a theoretical description of these observations explaining the emergence of the geostrophic mode by a "quartetic" resonance instability mechanism in which a primary wave is unstable together with a subharmonic wave produced by the triadic resonance instability of the primary wave.
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Maxime Brunet. Études expérimentales d'ondes d'inertie en régime non-linéaire : attracteurs et turbulence d'ondes. Mécanique des fluides [physics.class-ph]. Université Paris-Saclay, 2020. Français. ⟨NNT : 2020UPASS112⟩. ⟨tel-02923811⟩

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