Description du sujet de thèse

At the CNRS Futuroscope site, the Pprime Institute is recruiting a PhD student as part of a collaborative research initiative funded by the French National Research Agency (ANR) and DFG (Deutsche Forschungsgemeinschaft) and involving the Combustion Turbulente and Acoustique-Aérodynamique-Turbulence groups at the Pprime Institute, alongside the Laboratory for Flow Instabilities and Dynamics at TU Berlin.
This position concerns one PhD Thesis funded by ANR in the framework of DECRESCENDO, focusing on the high-fidelity simulation and analysis of flame dynamics and flame-generated sound in situation of lean hydrogen flames.

The proposed PhD Thesis focuses on (i) the high-fidelity numerical simulations of hydrogen/air flames and (ii) the analysis of the resulting databases to develop simplified models that capture flame dynamics and flame-generated sound. These models will be employed to design and validate sound-source identification techniques that will subsequently support experimental investigations conducted on an annular burner (Figueira da Silva, 2024). The results of that study reveal coupling between thermo-diffusive flame instability and sound generation. The PhD Thesis will involve the generation and analysis of high-fidelity numerical simulation databases of hydrogen flames in conditions comparable to those considered experimentally.

The computations will be performed with the CREAMS in-house solver (Martinez-Ferrer et al., 2014; Boukharfane et al., 2018) which solves the compressible Navier-Stokes equations for multi-component reactive flows. CREAMS is coupled to CVODE and EGLIB libraries, thus permitting the use of state-of-the-art representations of detailed chemistry and molecular transport.
Preliminary DNS computations of planar flames will be performed to assess the choices of (i) the molecular transport description and (ii) the chemical kinetic scheme. For the latter, the relevance of simplified-optimized chemical schemes (Le Boursicaud et al., 2022) will be tested as a possibility for computational cost reduction.
From a more general viewpoint, the computations will aim to recover specific effects encountered in hydrogen-air flames, such as fuel consumption increase induced by thermo-diffusive instabilities (Berger et al, 2022 and Berger et al., 2023) or super-equilibrium temperature levels caused by local fuel enrichment of the mixture (Gicquel et al., 2004).

In parallel to the generation of data, dedicated postprocessing tools will be used for data reduction and the development of simplified models for the key processes underpinning sound generation (Cavalieri et al., 2019). Post-processing will involve modal decomposition and sound-source identification via inversion techniques (using the sound field to infer characteristics of the sound-generation mechanisms).

- REQUIRED SKILLS:
The candidate must hold a Master's degree and/or an engineering degree.
Skills are expected in the fields of fluid mechanics, programming, numerical simulation, stability analysis and signal processing.

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* REFERENCES :
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L. Berger, A. Attili, H. Pitsch, Intrinsic instabilities in premixed hydrogen flames: parametric variation of pressure, equivalence ratio, and temperature. Part 2 – Non‐linear regime and flame speed enhancement, Combustion and Flame, 240 (2022) 111936
L. Berger, M. Grinberg, B. Jürgens, P.E. Lapenna, F. Creta, A. Attili, H. Pitsch, Flame fingers and interactions of hydrodynamic and thermodiffusive instabilities in laminar lean hydrogen flames, Proceedings of the Combustion Institute, 39 (2023) 1525-1534
R. Boukharfane, F. Ribeiro, Z. Bouali, A. Mura, A combined ghost-point-forcing / direct- forcing immersed boundary method (IBM) for compressible flow simulations, Computers & Fluids, 162 (2018) 91-112
A.V.G. Cavalieri, P. Jordan, L. Lesshafft, Wave-packet models for jet dynamics and sound radiation, Applied Mechanics Reviews, Vol. 71(2019) 080702
O. Gicquel, D. Thévenin, N. Darabiha, Influence of diffusion on super-equilibrium temperature in turbulent non-premixed hydrogen/air flames, Flow Turbulence and Combustion 73 (2004) 307-321
P.J. Martinez Ferrer, R. Buttay R., G. Lehnasch, A. Mura, A detailed verification procedure for compressible reactive multicomponent Navier-Stokes solver, Computers and Fluids, 89 (2014) 88-110
A. Mura, A. Techer, G. Lehnasch, Analysis of high-speed combustion regimes of hydrogen jet in supersonic vitiated airstream, Combustion and Flame, Vol. 239 (2022) 111552
L.F. Figueira da Silva, Stochastic characterisation of unstable lean hydrogen–air annular premixed flames, Combustion Theory and Modelling, Vol. 28 (2024) 317-343
M. Le Boursicaud, L. Carbajal Carrasco, Z. Bouali, A. Mura, Optimized two-step (OTS) chemistry model for the description of partially premixed combustion, Combustion and Flame, 245 (2022) 112287

Contexte de travail

The project addresses challenges in lean hydrogen combustion, with a specific focus on the acoustic phenomena generated by ultra-lean hydrogen/air flames. In contrast to other on-going projects dealing with thermoacoustic instability of flames in confined environment, it is focused on the root-cause of direct combustion noise and thus restricted to unconfined transitional and turbulent flames.

The PhD student will be based at the Institut Pprime on the ISAE-ENSMA site (https://pprime.fr/).

Le poste se situe dans un secteur relevant de la protection du potentiel scientifique et technique (PPST), et nécessite donc, conformément à la réglementation, que votre arrivée soit autorisée par l'autorité compétente du MESR.

Contraintes et risques

- Registration with the Doctoral School: ED-MIMME
- Short trips in France and abroad are to be expected as part of collaborative exchanges and conferences