Dynamically Dominant Subfilter-scale Structure for LES of Flame-Turbulence Interactions

A key weakness of large-eddy simulation (LES) of premixed turbulent combustion is its inability to predict key resolved-subfilter scale (RS-SFS) interactions that contribute to the full advective and chemical nonlinearities at first order levels. We explore the development of mathematical forms to approximate "dynamically dominant" (DD) SFS content of key species in key chemical nonlinearities for the key reactions within the species source terms, without the need for SFS grid support. Using DNS of 3D flame-turbulence interactions with large scale separation between integral/flame and flame/Kolmogorov scales, we identify the DD SFS content first in Fourier space by down-selecting from linear sums of nonlinear terms that contribute to RS-SFS interactions. From inverse-transformed structure in physical space, we find that the DD SFS species concentrations are localized to the lower curvature regions of the flame with two basic structural forms relative to the flame. The two relatively simple structural forms can be represented with 1D mathematical forms over discretized flame surfaces. We argue that these forms are likely generalizable to flame-turbulence interaction regimes more broadly. Key chemical nonlinearities miss over 40% of the SFS contributions to the source term that is reduced to less than 1% when the DD SFS contribution is included, suggesting a viable path to a new SFS modeling strategy for LES of premixed turbulent combustion.