Application of a flame-wrinkling les combustion model to a turbulent mixing layer

Abstract

The necessity for turbulent combustion modeling in the large-eddy simulation (LES) of premixed turbulent combustion is evident from the computational cost and the complexity of handling flame kinetics reaction mechanisms directly. In this paper, a new flame-wrinkling LES combustion model using conditional filtering is proposed. The model represents an alternative approach to the traditional flame-surface density based models in that the flame distribution is represented by a flame-wrinkle density function and that the effects of flame stretch and curvature are handled through a modeled transport equation for the perturbed laminar flame speed. For the purpose of validating the LES combustion model, LESs of isothermal and reacting shear layers formed at a rearward-facing step are carried out, and the results are compared with experimental data. For the isothermal case, the agreement between LES and the experimental data is excellent. For the reacting case, the evolution and topology of coherent structures is examined, and direct comparisons are made with time-averaged profiles of velocity and its fluctuations. temperature, and reaction products. Good agreement is obtained, to a large extent due to accurate modeling of the flame-wrinkle density but also to the novel treatment of the strain-rate effects on the laminar flame speed of the lean propane-air mixture.