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Instabilités thermoacoustiques dans les moteurs à propergol solide

Abstract : In a solid rocket motor, self-sustained thermo-acoustic instabilities, induced by the coupling of the combustion dynamics of aluminum droplets released by the burning propellant with the acoustic field can induce pressure oscillations.The analysis conducted throughout this manuscript relies thus on a set of simplifying hypothesis by assuming (i) that the response of the combustion of aluminum droplets to acoustic perturbations is controlled by the oscillating drag exerted by the local flow around the droplet, (ii) that this unsteady combustion process can be assumed quasi-steady for the range of frequencies and acoustic amplitudes studied and (iii) that aluminum combustion is abruptly quenched when the aluminum droplet diameter falls below a residual diameter.The thermo-acoustic instability is studied first by numerical flow simulations in a generic solid rocket motor and theoretical analyses. The post-combustion residual diameter of the aluminum particles, the amplitude of acoustic perturbation and the lifetime of the burning aluminum droplets are among the main parameters altering the instability. Also, three combustion response behaviors to acoustics are identified : a linear behavior for small acoustic pressure levels followed by a quadratic behavior then a highly non-linear behavior when the pressure amplitude increases in the motor chamber. Moreover, two important features of the response of aluminum droplets are identified. They are associated to oscillations of the droplet lifetime at the boundary of the droplet cloud and to fluctuations of the droplet evaporation rate, controlled by convection. The dynamics of the droplets highly depends on gas and droplet velocity fields and on droplet diameter. Taking these features into account, yields analytical expressions that allow to reproduce with accuracy the numerical results from the flow simulations. Four dimension less numbers are then identified. They govern the dynamics of these instabilities. Inspired from the previous theoretical analysis, a weakly nonlinear low-order numerical model is finally developed to predict limit cycles.
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Submitted on : Wednesday, September 4, 2019 - 12:31:07 PM
Last modification on : Friday, October 23, 2020 - 5:03:45 PM
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  • HAL Id : tel-02278347, version 1


Aurélien Genot. Instabilités thermoacoustiques dans les moteurs à propergol solide. Mécanique des fluides [physics.class-ph]. Université Paris-Saclay, 2019. Français. ⟨NNT : 2019SACLC032⟩. ⟨tel-02278347⟩



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