Gradient and Counter-Gradient Modeling in Premixed Flames: Theoretical Study and Application to the LES of a Lean Premixed Turbulent Swirl-Burner

This paper concerns the modeling of unresolved turbulent fluxes in premixed flames. Classically closed with a gradient assumption, this term may also contain a counter-gradient part, as detailed in other works. In a first section, the bibliographical resources giving details about the closure of the unresolved turbulent fluxes are investigated and confronted thanks to time-averaged direct numerical simulation databases. Large-eddy simulation is then performed to underline the possibility to integrate the counter-gradient transport in an industrial-like computation where the mesh may not be thin enough to capture all the turbulent transport at a resolved scale. Results given by the considered closures are compared with experimental points and analyzed.