LES of turbulent combustion: On the consistency between flame and flow filter scales

A recurrent issue in premixed combustion LES is that the flame thickness is smaller than the grid size. Broadening of the reactive layer is then mandatory to ensure a proper propagation of the filtered flame front. The reactive flow governing equations exhibit then two filter operators of different sizes dedicated to the flow field and the flame front, respectively. The consistency issues between flame and flow filter sizes in LES of turbulent premixed flames are discussed in the present article. A general mathematical formalism considering two different filter sizes is proposed. A new closure of the resulting LES balance equations system is derived in the framework of the Filtered TAbulated Chemistry for LES (F-TACLES) formalism. The new model, called F2-TACLES, is first validated by computing 1-D premixed filtered flames. Then an LES of the complex turbulent premixed PRECCINSTA swirl burner is successfully performed. In particular, the new model formulation improves the prediction of resolved flame/turbulence interactions.