Subcritical and supercritical dynamics of incompressible flow over miniaturized roughness elements

Abstract : This thesis aims at highlighting the limits of passive control by usingminiaturized roughness elements. The flow topology induced by the presence ofcylindrical roughness and miniaturized vertex generators has been studied to uncover asymptotic and short time dynamics. Supercritical bifurcations has been investigated by means of global stability analysis. Subcritical bifurcation are induced by transient growth of the energy or receptivity of stable global modes. 3D optimal forcing structures are extracted to figure out the spatial distribution linked to the resonant pulsation. Perturbed direct numerical simulation reveals the pivotal role of the less steady global mode in the non-linear unsteadiness. A detailed analysis of the flowstructures is provided and linked to the involved linear mechanisms. Global feature of the eigenmode are linked to the presence of the separation zone behind the cylindrical roughness. By using miniaturized vortex generators the separation zone is suppressed and no isolated global modes are present. The flow dynamics turns out to be driven not only by roughness Reynolds number and geometrical aspect ratio but also by the ratio between the roughness height and the boundary layer thickens.
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Michele Alessandro Bucci. Subcritical and supercritical dynamics of incompressible flow over miniaturized roughness elements. Fluids mechanics [physics.class-ph]. Ecole nationale supérieure d'arts et métiers - ENSAM, 2017. English. ⟨NNT : 2017ENAM0053⟩. ⟨tel-01881371⟩

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