Mixing models and turbulence-radiation interactions in nonpremixed jet flames via the LES/FMDF approach

Recent RANS predictions of extinction in turbulent jet flames using the PDF transport model have shown sensitivity to the mixing model and the mixing frequency when attempting to predict Sandia Flames D, E, and F. Extensions of such studies in the context of LES using the filtered mass density function (FMDF) approach are considered here for idealized versions of these flames using one-step global chemical kinetics. Results are shown from the IEM, MC, and EMST mixing models for a range of Reynolds numbers and the effect of mixing frequency is explored. Similarities and differences regarding these trends are compared to previous RANS findings. Also, we extend the LES/FMDF approach to consider luminous radiation from soot. A simple soot volume fraction state relationship is used to introduce transient soot layers into an idealized acetylene-air flame. A novel parallelization of the discrete ordinates method (DOM) is introduced to solve the filtered radiative transfer equation with subgrid-scale turbulence-radiation interactions handled by an extension of the FMDF approach. The importance of subgrid-scale turbulence-radiation interactions and aspects of strongly radiating flame structure are highlighted. This study also paves the way for inclusion of more realistic soot transport and kinetics models for future studies of soot control strategies as well as other important applications.