Mission
During the lift-off phase, the propulsive jets that are supersonic, hot, imperfectly expanded and with a chemical composition distinct from that of the ambient air, generate thermal stresses on the launch pad infrastructure, as well as high acoustic
levels which induce high loads on the launcher and its payload. These constraints are key factors in the design of the launcher and its launch pad. Water injection is therefore commonly used on the launch pad to reduce them.
For several years, ONERA has been developing validated numerical tools and models, representative of the various phenomena (transient, aerodynamic, thermal, acoustic and two-phase flows) encountered during the launch and return to the ground of
reusable launcher stages. Thermal simulations take into account time and spatial scales in both solid and fluid zones. Acoustic simulations are based on a direct calculation of the sources and their propagation in the far field thanks to a two-way
coupling between a Navier-Stokes solver and an Euler solver. This approach, implemented during a previous ONERA/CNES PhD, takes into account the non-linear effects induced by high acoustic levels. Taking liquid water into account requires a
multi-scale approach: a dense phase at the water nozzle outlet followed by atomization into droplets and a two-phase dispersed regime. This modelling work, initiated in another previous ONERA/CNES PhD, needs to be pursued and is the subject of this PhD work.
The aim is to extend the numerical simulation methodology described above to situations where water injection is used. One of the mechanisms by which water injection affects the acoustic and thermal environment on the launch pad is the
modification at the source of the aerodynamic and thermal structure of the propulsive jets. The first step of this PhD will involve the evaluation and development of multi-phase models (run back, spraying, atomization, fog, etc.), and physical models
(heating, drag, evaporation, etc.), to determine their influence on acoustics and thermics.
To provide validated methodologies that are representative of these interacting multiphysical phenomena, the PhD student will use test-cases of increasing complexity. The first level of validation will be based on academic cases. The second level will aim at validating the numerical approaches on simple applied cases corresponding to controlled tests. These tests are being carried out as part of an internal ONERA research project. Lastly, the Projet d’IntĂ©rĂŞt Commun currently in progress with CNES provides access to a wealth of experimental data from the MARTEL test bench (a reduced scale device generating jets from H2/air combustion) at the Institut P’ in Poitiers. New experimental techniques for characterizing the dispersed phase are being developed as part of an ongoing P’/CNES thesis, and will benefit this PhD work.
Once the physics has been understood and the simulation methodology established, numerical parameterizations in parallel with those performed experimentally (variation of mass ratios, momentum, etc.) will be carried out with the ultimate aim of
optimizing the reduction of acoustic and thermal levels. The analysis of simulation results and comparisons with experiments will lead to scientific communications and publications.
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For more Information about the topics and the co-financial partner (found by the lab !);
contact Directeur de thèse – christophe.bogey@ec-lyon.fr
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 !
Profil
Fluid mechanics
Laboratoire
ONERA
Message from PhD team
More details on CNES website : https://cnes.fr/fr/theses-post-doctorats
