Fluid Mechanics and Acoustics Laboratory - UMR 5509

LMFA - UMR 5509
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Lyon
France


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Soutenance de thèse ECL

Smail Lebbal

Mardi 7 décembre 2021, 14h30, amphi 3, bât. W1, ECL

Smail Lebbal

Dynamique des écoulements pulsés dans des canaux déformables

Jury omposition
Frédéric Alizard, MCF HDR, LMFA, Directeur de thèse
Damien Biau, MCF Arts et Métiers, Paris, Examinateur
Christopher Davies, Prof. Univ. Leicester, Rapporteur
Uwe Ehrenstein, Prof. Univ. Aix-Marseille, Rapporteur
Benoît Pier, DR CNRS, LMFA, Directeur de thèse
Florence Raynal, CR CNRS, LMFA, Examinatrice

Abstract

In this study, the linear instability of steady and pulsatile flows in deformable channels is investigated. The compliant wall model consists of a spring-backed plate including a damping mechanism. At the interface between the fluid and the walls, all viscous stresses and pressure forces are taken into account. The analysis of steady configurations proceeds via classical eigenvalue methods, while a complete Floquet analysis is implemented for pulsatile configurations, including an efficient approach for removing the spurious modes. The results obtained include the dynamics of Tollmien-Schlichting (TS) modes as well as flow-induced surface instability (FSI) modes, in the form of both traveling wave flutter (TWF) and divergence (DIV) modes. The different instability modes are then reinterpreted in the light of four main dimensionless control parameters: Reynolds number (Re), Womersley number (Wo), amplitude of the base flow modulation and the reduced velocity (VR) which represents the response of the flexible wall to hydrodynamic loading. The complete instability characteristics are systematically investigated over large regions of the multi-dimensional control parameter space. It is observed that TWF modes are primarily governed by VR and largely independent of Re, while DIV and TS modes are both affected by VR and Re. It is found that the instability is generally dominated by the TWF mode of varicose symmetry, for steady as well as pulsatile conditions. A new transition mode has been discovered, resulting from the coalescence of two Floquet modes. Close monitoring of energy transfer processes provides physical insight into the different mechanisms driving each class of modes.

JPEG - 146.4 kb
Pulsatile channel flow with infinite spring-backed flexible walls.

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