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PhD defense : LUC POTIER – “Large Eddy Simulation of the combustion and heat transfer in sub-critical rocket engines”

  Thursday 24 May 2018 at 14h00

  Phd Thesis       Salle de conférence Jean-Claude ANDRE    

Abstract

Combustion in cryogenic engines is a complex phenomenon, involving either liquid or supercrit- ical fluids at high pressure, strong and fast oxidation chemistry, and high turbulence intensity. Due to extreme operating conditions, a particularly critical issue in rocket engine is wall heat transfer which requires efficient cooling of the combustor walls. The concern goes beyond mate- rial resistance: heat fluxes extracted through the chamber walls may be reused to reduce ergol mass or increase the power of the engine. In expander-type engine cycle, this is even more important since the heat extracted by the cooling system is used to drive the turbo-pumps that feed the chamber in fuel and oxidizer. The design of rocket combustors requires therefore an accurate prediction of wall heat flux. To understand and control the physics at play in such combustor, the Large Eddy Simulation (LES) approach is an efficient and reliable numerical tool. In this thesis work, the objective is to predict wall fluxes in a subcritical rocket engine configuration by means of LES. In such condition, ergols may be in their liquid state and it is necessary to model liquid jet atomization, dispersion and evaporation.The physics that have to be treated in such engine are: highly turbulent reactive flow, liquid jet atomization, fast and strong kinetic chemistry and finally important wall heat fluxes.

This work first focuses on several modeling aspects that are needed to perform the target simu- lations. H2/O2 flames are driven by a very fast chemistry, modeled with a reduced mechanism validated on academic configurations for a large range of operating conditions in laminar pre- mixed and non-premixed flames. To FORM the spray issued from the atomization of liquid oxygen (LOx) an injection model is proposed based on empirical correlations. Finally, a wall law is employed to recover the wall fluxes without resolving directly the boundary layer. It has been specifically developed for important temperature gradients at the wall is validated on turbulent channel configurations by comparison with wall resolved LES.

The above models are then applied first to the simulation of the CONFORTH sub-scale thrust chamber. This configuration studied on the MASCOTTE test facility (ONERA) has been mea- sured in terms of wall temperature and heat flux. The LES shows a good agreement compared to experiment, which demonstrates the capability of LES to predict heat fluxes in rocket com- bustion chambers. Finally, the JAXA experiment conducted at JAXA/Kakuda space center to observe heat transfer enhancement brought by longitudinal ribs along the chamber inner walls is also simulated with the same methodology. Temperature and wall fluxes measured with smooth walls and ribbed walls are well recovered by LES. This confirms that the LES methodology proposed in this work is able to handle wall fluxes in complex geometries for rocket operating conditions.

Jury

E. LAMBALLAIS             UNIVERSITÉ DE POITIERS                                                          Referee

S. DUCRUIX                  EM2C  – CNRS, UPR 288                                                               Referee

F. NICOUD                    IMAG – UMR CNRS 5149                                                                Member

O. DESJARDINS           SIBLEY SCHOOL OF MECHANICAL & AEROSPACE ENG.         Member

Ph. GRENARD               ONERA                                                                                            Member

D. SAUCEREAU           ARIANEGROUP                                                                              Member

J. PICHILLOU                CNES                                                                                              Invited member

B. CUENOT                   CERFACS                                                                                       Advisor

F.  DUCHAINE              CERFACS                                                                                       Co advisor