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Cascades d’énergie et turbulence d’ondes dans une expérience de turbulence en rotation

Abstract : We present an experimental study of the effect of global rotation on statistically stationary turbulent flows. In a first experiment, the flow is generated with counter-rotating vortex generators acting in a periodic motion in a rotating tank filled with water. Resolved in time measurements of the three component of the velocity are performed, in both horizontal and vertical planes, thanks to a stereoscopic particle image velocimetry system embarked in the rotating frame. The flow has, in accordance with the bibliography, a strong anisotropy and shows the emergence of an energetic 2D flow. For the first time experimentally, we describe the global scale by scale energy budget of a rotating turbulence through the measure of the terms of the inhomogeneous generalization of Kármán-Howarth-Monin equation. We thus reveal a double energy cascade: direct at small scale and inverse at large scale, the scale of cascade reversal decreasing with the rotation rate. Then, we evaluate the injected power into the system which is intrinsically linked to the inhomogeneities of the flow. The energy input comes from auto-advection of turbulent structures through the boundaries of the area considered. It is broadband in scales and spreads as ration increases. We then focus on relevance of inertial wave turbulence models. We first perform a spatiotemporal analysis which reveals the presence of linear inertial waves at large frequencies and scales. However, we show that the spatiotemporal signature of small frequencies and scales are scrambled by the linear process of stochastic sweeping by the 2D energetic mode. In a second experiment, the flow is created thanks to a four-rectangular-blade impeller in a closed rotating tank. We estimate the energy dissipation rate through the measure of the injected power by the motor that drives the impeller. We then bring, for the first time, a direct evidence of the scaling law predicted by inertial wave turbulence models which is fallen by a factor Rossby compared to the scaling law of 3D homogeneous isotropic turbulence.
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Submitted on : Tuesday, September 1, 2015 - 12:27:06 PM
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Antoine Campagne. Cascades d’énergie et turbulence d’ondes dans une expérience de turbulence en rotation. Dynamique des Fluides [physics.flu-dyn]. Université Paris Sud - Paris XI, 2015. Français. ⟨NNT : 2015PA112116⟩. ⟨tel-01189585⟩

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