002 Study of the role of aluminum droplets in solid rocket motor acoustics

Job title:

002 Study of the role of aluminum droplets in solid rocket motor acoustics

Company:

Centre National d’Etudes Spatiales

Job description

25-002 Study of the role of aluminum droplets in solid rocket motor acousticsPostuler25-002 Study of the role of aluminum droplets in solid rocket motor acoustics

• Doctorat, 36 mois
• Temps plein
• Indifférent
• Maitrise, IEP, IUP, Bac+4
• Propulsion

PostulerMissionLike any propulsion system, solid rocket motors are frequently submitted to operating instabilities [1]. Recent motors such as the P80 or the P120C of the VEGA and Ariane 6 launchers are no exception to this observation. This is mainly due to the release, during the solid propellant combustion, of a large quantity of energy in a relatively small volume. The diversion of a very small part of this energy into localized fluctuations of velocity and pressure is enough to generate larger instabilities that almost always end up being organized around preferred frequencies linked to the internal geometry, in this case the frequencies of the acoustic modes of the combustion chamber. In a solid rocket motor, the latter is often elongated so that the acoustic modes involved are mainly the longitudinal modes. Low-amplitude pressure oscillations can thus result in significant thrust oscillations which, even if they rarely threaten the integrity of the motor or the launcher via a coupling with the natural modes of the structure, nevertheless constitute a source of annoying or even harmful vibrations for the payload and equipment. For example, for the Ariane 5 P230, the relative amplitude of thrust fluctuations was estimated at around 5% for a relative amplitude of the measured pressure fluctuations not exceeding half a percent [2].In these motors, the transformation during combustion of the energy stored in molecular bonds into mechanical energy and the dynamics of the flow of combustion products often play an active role in triggering instabilities. If the role of combustion is predominant, they are named combustion instabilities. If the flow is the main factor, we talk about hydrodynamic instabilities, for which vortices appear in the combustion chamber. This distinction is convenient for classifying instabilities but, in practice, we suspect the existence of connections between these different mechanisms so that it is not always easy to identify the origin of the instability and its promoter. A motor can also develop several kind of instabilities during operation, for example an instability of hydrodynamic origin at the start of firing then combustion instabilities thereafter, as predicted on the P120C and P80 thrusters [3,4], or even two types of coupled hydrodynamic instabilities, as interpreted on the P230 of Ariane 5 [5].In the context of this thesis, we will focus on the combustion instability of aluminum droplets (released during the combustion of solid propellant) [6], to which we will superimpose a hydrodynamic instability generating vortices in the combustion zone of the aluminum droplets.To study this triple interaction (acoustics – burning dropets – vortices), the following thesis schedule is considered: (1) Numerical simulations to evaluate the effects of aluminum combustion models and the presence or absence of vortices, (2) Analytical development of a flame transfer function validated by simulation for new aluminum combustion models, without vortices (see for example [7]), (3) Analyses, assisted by acoustic energy balance [8], of the acoustics – droplets – vortices coupling, for reactive or inert droplets, in the simulations carried out.We seek for a highly motivated PhD student to produce multiple publications submitted to international peer-reviewed journals, presenting simulation results, with scaling laws assisted by dimensional analyses, and analytical models. The PhD student will also be encouraged to participate in international conferences.[1] Kuentzmann, P. (2002). Introduction to solid rocket propulsion. NATO technical report RTO-EN-023[2] Scippa, S., Pascal, P., & Zanier, F. (1994). Ariane 5-MPS-Chamber pressure oscillations full scale firing results: Analysis and further studies. In 30th Joint propulsion conference and exhibit (p. 3068).[3] Larrieu, S., Orlandi, O., Godfroy, F., & Di Trapani, C. (2018). Two minutes inside P120C SRM. Space Propulsion.[4] Grossi, M., Bianchi, D., & Favini, B. (2022). Investigation of Q1D Model for Pressure Oscillations in Solid Rocket Motors, In 9ᵀᴴ EUCASS.[5] Lupoglazoff, N., Vuillot, F., Dupays, J., & Fabignon, Y. (2000, November). Numerical simulations of the unsteady flow inside Ariane 5 P230 SRM booster with burning aluminum particles. In 2nd European Conference on Launcher Technology, Rome, Italy.[6] Genot, A. (2019). Instabilités thermoacoustiques dans les moteurs à propergol solide (Doctoral dissertation, Université Paris Saclay (COmUE)).[7] Genot, A., Gallier, S., & Schuller, T. (2019). Model for acoustic induced aluminum combustion fluctuations in solid rocket motors. Journal of Propulsion and Power, 35(4), 720-735.[8] Radenac, E. (2013). Fluctuating energy balance for post-processing multiphase flow computations. Journal of Propulsion and Power, 29(3):699-708.For more Information about the topics and the co-financial partner (found by the lab !); contact Directeur de thèse –Then, prepare a resume, a recent transcript and a reference letter from your M2 supervisor/ engineering school director and you will be ready to apply online before March 14th, 2025 Midnight Paris time !

Expected salary

Location

Toulouse

Job date

Wed, 05 Feb 2025 05:46:08 GMT

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