Turbulence-radiation interactions in large-eddy simulations of luminous and nonluminous nonpremixed flames

Abstract

Turbulence-radiation interactions (TRI) are explored in large-eddy simulations (LES) of luminous and nonluminous nonpremixed jet flames. The simulations feature a transported filtered density function (FDF) method for subfilter-scale fluctuations in composition and temperature, and a fully coupled photon Monte Carlo (PMC) method for radiative transfer with line-by-line (LBL) spectral resolution. The model is exercised to isolate and quantify individual contributions to TRI for conditions that range from small optically thin flames to relatively large optically thick flames, including spectral molecular gas radiation and broadband soot radiation. The results provide new physical insight into TRI and guidance for modeling. In all cases, emission TRI are responsible for a significant fraction of the radiative emission, and that fraction increases with increasing optical thickness. For simulations where 84% of the turbulence kinetic energy is resolved, contributions of subfilter-scale fluctuations to emission TRI exceed those of resolved-scale fluctuations. The largest contributions to emission TRI are the absorption coefficient–temperature correlation and the temperature self-correlation. Absorption TRI are evident only for relatively high optical thicknesses. In all cases, the contributions of subfilter-scale fluctuations to absorption TRI are negligible.