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Theses

Mechanisms of instabilities of high-frequency combustion and application in engines-rockets

Abstract : This thesis presents a study of high frequency instabilities in rocket engines. This issue, which has plagued many engine development programs, is approached by three complementary viewpoints: experimental, theoretical, and numerical. First, experiments are carried out to identify the main processes involved and bring forth mechanisms taking place when an engine becomes unstable. To achieve this stage, a new modulator (the VHAM), capable of creating acoustic waves representative of what occurs in an actual engine, is designed and characterized. The second part of this thesis concern theoretical analysis. Two models are developed following the main conclusions of the experimental campaign: heat release oscillations are due to the transverse flames’ motion, and the phenomenon is triggered when droplets become small enough to be convected by the acoustic field. Using these models as a baseline, a numerical code (STAHF) is presented. Its purpose is to account for mechanisms identified previously for little computational cost. This code is validated on particularly responding situations observed during experiments. It is then shown that it can be used to study real scale rocket engines. The third point of view adopted to address the problem is numerical simulation. Full compressible LES is chosen to study the interaction between acoustics and combustion. A new combustion model for non-premixed flames with infinitely fast chemistry is presented and validated on a well documented flame (H3). It is then used to study the interaction between a transverse acoustic wave and the H3 flame. A comparison between the Rayleigh source term computed from the simulation and the one predicted by the theoretical model FAME is conducted eventually.
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  • HAL Id : tel-02637918, version 1

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Yoann Méry. Mechanisms of instabilities of high-frequency combustion and application in engines-rockets. Other. Ecole Centrale Paris, 2010. English. ⟨NNT : 2010ECAP0012⟩. ⟨tel-02637918⟩

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