Descriptif et objectifs de l'emploi :
Context:

Large eddy simulation (LES), where the largest turbulent motions in the flow are explicitly computed while only the effects of smaller ones are modelled, is a very powerful tool for numerical simulations of turbulent combustion systems. This technique gives access to timeresolved information and is then well suited to predict and investigate combustion instabilities in burners or cycle-to-cycle variations in internal combustion engines. Subgrid scale models are required both for turbulent transport and chemical reactions.

Various combustion models have been developed and tested (probability density function, flame surface density, thickened flame model...) but very few automatically determine the model parameters from the knowledge of large resolved scales. Such dynamic procedures have been found very successful to predict unresolved transport in non-reacting flows (Germano dynamic model, Germano et al.). Unfortunately, phenomena are very different: combustion mainly occurs at unresolved scales, whereas resolved flow motions contain most of the turbulent kinetic energy. Adapted dynamic formulations are then required to avoid illposed problems (Charlette et al. or Knikker et al.). Another practical difficulty is encountered when implementing dynamic approaches in a LES solver running on massively parallel machines. The resolved fields should be filtered at a test filter scale, a time-consuming operation that is not obvious when solving balance equations on unstructured meshes. An alternate approach could be to determine model parameters outside of the LES solver, in a second code coupled to it through an adapted framework such as CORBA or PALM. Note also that model parameters do not need to be updated at each time step.


Proposed work:

This available post-doctoral position (up to 15 months) enters a project funded by Agence Nationale de la Recherche of Franch Minister of Research and devoted to multi-cycle large eddy simulations of the reacting flow field in a multi-cylinder internal combustion engines.
Cited references:

F. Charlette, C. Meneveau and D. Veynante

A power-law wrinkling model for LES of premixed turbulent combustion. Part I : Non-dynamic formulation and initial tests, Part II : Dynamic formulation.

Combustion and Flame, 131 (1/2), pp 159-197, 2002.

M. Germano, U. Piomelli, P. Moin and W. Cabot

A dynamic subgrid-scale eddy viscosity model for large eddy simulation of turbulent premixed combustion.

Physics in Fluids A, 3 (111), 1760 - 1765, 1991.

R. Knikker, D. Veynante and C. Meneveau

A dynamic flame surface density model for large eddy simulation of turbulent premixed combustion.

Physics in Fluids A, 16 (111), l91 - L94, 2004.

R. Gonçalves dos Santos, M. Lecanu, S. Ducruix, O. Gicquel, E. Iacona and D. Veynante

Coupled large eddy simulations of turbulent combustion and radiative heat transfer.

Combustion and Flame, 152, 387 - 400, 2008.