Analyse théorique et contrôle des instationnarités dans un écoulement de culot en régime compressible.

Abstract : This thesis is a contribution to the study of the dynamics and control of large-scale oscillations that develop in the subsonic regime in the lee of bodies of revolution modeling the first stage of a launcher. For several configurations (disk, sphere, axisymmetric blunt base), the steady/unsteady transition is characterized b means of a stability analysis of the axisymmetric flow at low Reynolds numbers. We first show that the existence of such oscillations is intimately connected to a local transition to absolute instability in the nearwake. The subsequent results rely on a global approach of stability, better suited to nonparallel flows. The class of flows under consideration exhibits a single sequence of bifurcation, involving a stationary mode and a low-frequency oscillating mode. An analysis based on the normal form theory shows that the sharp frequency and spatial pattern selection exhibited by t! he flow at the onset of unsteadiness depend on the leading-order nonlinear interaction of the leading eigenmodes. We also demonstrate that an increase in the compressibility weakens the production of perturbations and enhances their downstream advection, both effects being stabilizing. A sensitivity of eigenvalues to a steady forcing finally allows to develop a systematic approach of open-loop control in compressible flows. This approach has been applied to the blunt base, an investigation which stands as a step towards the full control of afterbody flow unsteadiness. Various methods are considered, including additional control devices, heat sources, and fluid blowing through the base («base bleed»).
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Theses
Mechanical engineering. Ecole Polytechnique X, 2008. French


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Submitted on : Wednesday, July 21, 2010 - 12:50:39 PM
Last modification on : Wednesday, July 28, 2010 - 10:00:15 AM

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Philippe Meliga. Analyse théorique et contrôle des instationnarités dans un écoulement de culot en régime compressible.. Mechanical engineering. Ecole Polytechnique X, 2008. French. <pastel-00004529>

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