An a priori analysis of the structure of local subfilter-scale species surrounding flame fronts using direct numerical simulation of turbulent premixed flames

An a priori analysis of subfilter-scale (SFS) species structure important to estimate chemical reaction rates in large-eddy simulation (LES) is performed using direct numerical simulation (DNS) of a turbulent premixed flame at a turbulence Reynolds number R e 0 = 329 and Karlovitz number K a 0 = 7.23 with semi-detailed finite-rate chemistry. Differences between the complete chemical reaction rates extracted from DNS and those estimated from LES-filtered variables are quantified. The spatial distributions of these differences are found to be localized in regions surrounding the flame front for representative reactions. Within these regions, variations in the localization relative to the flame, scale, and magnitude of the SFS species concentrations are quantified, and mean SFS structure is determined. SFS species structure is found in two groupings: "single-banded"structure characterized by one distinct peak and "double-banded"structure characterized by two peaks of opposite signs. Species that are produced and consumed within the flame such as CH 2 O and HCO are observed to have single-banded structure, and species displaying a frontal behavior such as n-C7H16 and OH are found to have double-banded structure, on average. The local SFS structure surrounding the flame is impacted by neighboring flame-flame interactions as well as by variations in flame curvature. The impacts of the flame-flame interactions are strong when the SFS species structure has "large"length scales with concentration peaks significantly displaced from the flame front. Curvature effects are shown to be strong in high curvature regions of the flame.