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Apparition de rugosités de surface lors de l'ablation d'un matériau composite en régime de transition entre laminaire et turbulent

Abstract : During the descent of an atmopheric reentry vehicle, very high pressure and heat flux (> 2000 K) is reached at the surface of the body. In order to withstand these extreme conditions, thermal protective systems are used. These are composed of carbon-carbon composite materials. Numerous phenomena will occur at the material surface, including heterogeneous chemical reactions of oxidation and nitriding of the carbon. In the most extreme cases, sublimation will also occur. These reactions will lead to the ablation of the thermal protection.Along the different flow regimes from laminar to turbulent, a multiscale roughness will be developed on the material. The laminar regime is associated with a microscopic roughness due to the architecture of the carbonated composite. This surface condition will then favour locally the laminar to turbulent transition, leading to macroscopic structures, of the centimeter scale. Finally when the turbulence is fully developed, regular waves appear no more localised but this time generalised to the whole surface. These characteristic patterns are known as "scallops". They are able to multiply the heat transfer and the recession rate by more than 2; therefore understanding their formation and behaviour is a necessity for a better design of the thermal protection.A numerical approach has been considered in order to identify the stability regimes of a surface perturbation according to the flow regime, the micro-roughness of the material, and its reactivity. The code SURRF, based on the open-source software OpenFOAM was developed in this context. Thanks to the turbulence model gamma-Re_th which models the laminar-turbulence transition, the parameters which enable the development and growth of the scallops at the material surface were determined.
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Submitted on : Friday, September 4, 2020 - 2:30:10 PM
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Xavier Lamboley. Apparition de rugosités de surface lors de l'ablation d'un matériau composite en régime de transition entre laminaire et turbulent. Matériaux. Université de Bordeaux, 2019. Français. ⟨NNT : 2019BORD0334⟩. ⟨tel-02930613⟩

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