Dominant Subfilter-Resolved Scale Flame-Turbulence Advective Nonlinearities in LES of Premixed Turbulent Combustion

Central to the LES framework is the need to model nonlinear interactions between variance-dominant resolved-scale (RS) motions and subfilter-scale (SFS) fluctuations. A central feature of premixed turbulent combustion is nonlinear flame-turbulence interactions, a key element of which is advective nonlinearity in momentum, energy and species generation. Here we extract the dominant SFS-RS advective nonlinear interactions to isolate SFS content that underlies the evolution of the resolved scales for encapsulation within mathematical forms for potential use in advanced modeling strategies. Our approach uses the triadic structure of the second-order advective nonlinearity within the  multi-dimensional Fourier scale decomposition, applied here to “reduced physics” simulations of flame-vortex interactions with a new method for analysis of inhomogeneous turbulence in multi-dimensional Fourier-space. We determine the kinematic relationships between coherent physical-Fourier space structure. From these we extract the dominant triadic advective SFS-RS couplings in flame-turbulence dynamics which we find to be localized in spectral space to near the SFS-RS interface. In physical space we find the dominant SFS content to be localized near the thin flame heat-release zone. Supported by AFOSR