Meliga, Philippe (2008) A theoretical approach for the onset and control of unsteadiness in compressible afterbody flows. PhD thesis ONERA/DAFE, ONERA/DAFE, EP/X p.232.
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Alternative Locations: http://www.imprimerie.polytechnique.fr/Theses/Files/Meliga.pdf
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»).
| Item Type: | PhD Thesis (PhD) |
|---|---|
| PhD Supervisor: | Chomaz, Jean-Marc |
| Date: | 18 November 2008 |
| Board of examiners: | Jean-Paul, Bonnet and Jeffrey, Crouch and Dan, Henningson and Hadrien, Lambaré and Jacques, Magnaudet and Pierre, Sagaut and Denis, Sipp |
| Ecole Doctorale: | ED 447 ECOLE DOCTORALE DE L'ECOLE POLYTECHNIQUE |
| Discipline: | ONERA/DAFE |
| Collection (Fonds): | Ecole Polytechnique (EP/X) |
| Institution: | EP/X |
| Department: | ONERA/DAFE |
| Subjects: | 4. Materials Science, Mechanics and Mechanical Engineering |
| Uncontrolled Keywords: | Compressible flows, Axisymmetric wakes, Convective, Absolute instability, Global stability, Normal forms, Adjoint methods, Sensitivity analysis, Open-loop control, Ecoulements compressibles, Sillage axisymétrique, Instabilité convective, Absolue, Stabilité globale, Formes normales, Méthodes adjointes, Analyse de sensibilité, Contrôle en boucle ouverte |
| ID Code: | 4529 |
| Deposited By: | Laurence Vidament |
| Deposited On: | 05 January 2009 |
Table of content
1 - Introduction
2 - Absolute instability in compressible axisymmetric wakes
3 - Global modes in the wake of axisymmetric bodies
4 - Global mode interaction & pattern selection in the wake of a disk
5 - Global modes in a compressible afterbody flow
6 - A step towards the control of afterbody flow unsteadiness
7 - Épilogue 215
Bibliography 227
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