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Convection forcée radiativement : du régime de Rayleigh-Bénard au régime ultime

Abstract : In this manuscript, we study convection driven by radiative heating. Radiative heating occurs in natural flows inside stars, supernovae, frozen lakes, and the Earth’s mantle. The heat source is partially volumic, which means that heat is directly injected in the turbulent flow itself, in contrast with the more classical Rayleigh-Bénard convection, where heat is injected through thermal conduction between the fluid and a solid plate. We focus on the case where the heat source decreases exponentially with the height inside the fluid. We study this problem numerically in the first part of the manuscript, before describing an experimental setup that realizes this type of heat source in the second part.We observe numerically and experimentally that the efficiency of thermal convection (in terms of dimensionless heat flux) depends strongly on the spatial extension of the heat source, with a clear-cut transition between two regimes.When the heat is injected on a typical height smaller than the boundary layer thickness, we recover the classical Rayleigh-Bénard régime of convection; the injected heat must diffuse through the boundary layers, which limits the overall heat transfer efficiency.When the heat is injected on a typical length larger than the boundary layer thickness, this limitation does not apply anymore, and we observe a much more efficient regime of heat transfer, predicted in the 60s by Spiegel and Kraichnan, and sometimes referred to as the « ultimate » regime of thermal convection.
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https://tel.archives-ouvertes.fr/tel-03124402
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Submitted on : Thursday, January 28, 2021 - 4:38:07 PM
Last modification on : Tuesday, January 4, 2022 - 4:27:53 AM
Long-term archiving on: : Thursday, April 29, 2021 - 7:52:16 PM

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  • HAL Id : tel-03124402, version 1

Citation

Simon Lepot. Convection forcée radiativement : du régime de Rayleigh-Bénard au régime ultime. Dynamique des Fluides [physics.flu-dyn]. Université Paris Saclay (COmUE), 2018. Français. ⟨NNT : 2018SACLS590⟩. ⟨tel-03124402⟩

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