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Theses

Instabilité globale linéaire et non linéaire d'écoulements de couche limite attachées ou décollées sur une plque plane

Abstract : The aim of this thesis is to describe the linear and non-linear dynamics of both attached and separated boundary-layer flows over a flat plate at low Reynolds numbers. The linear dynamics, driven by the interactions among the non-orthogonal eigenvectors, is studied using two global instability approaches: the global eigenvalue analysis and the direct-adjoint optimization. In these global instability analysis no spatial structure is assumed a-priori for the perturbation, and the convective effects due to the high non-parallelism of the flow are taken into account. In the case of the separated boundary-layer flows, it has been clarified the role of the following features in the onset of unsteadiness: i) the strong two-dimensional convective amplification; ii) the non-normality effects such as the 'flapping' phenomenon; iii) the high sensitivity to external forcing; iv) the globally unstable three-dimensional mode. Concerning the attached boundary layer, the aim has been to identify localized perturbations characterized by more than one frequency in the streamwise and/or spanwise direction, inducing a strong energy amplification. In order to assess the effects of non-linearity on the instability mechanisms identified by the global linear stability analysis, direct numerical simulations have been performed in a two- and three-dimensional framework for both the attached and separated boundary-layer flows. The dynamics of the perturbations which most easily brings the flows on the verge of turbulence have been studied. Different scenarios of transition have been observed, and the mechanisms leading the flow to turbulence have been analyzed in detail.
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https://pastel.archives-ouvertes.fr/pastel-00006225
Contributor : Ecole Arts Et Métiers Paristech <>
Submitted on : Tuesday, July 6, 2010 - 8:00:00 AM
Last modification on : Friday, July 17, 2020 - 2:56:30 PM
Long-term archiving on: : Thursday, March 30, 2017 - 5:55:06 AM

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  • HAL Id : pastel-00006225, version 1

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Stefania Cherubini. Instabilité globale linéaire et non linéaire d'écoulements de couche limite attachées ou décollées sur une plque plane. Sciences du Vivant [q-bio]. Arts et Métiers ParisTech, 2010. Français. ⟨NNT : 2010ENAM0012⟩. ⟨pastel-00006225⟩

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