Application of a Flame-wrinkling Les Combustion Model to a Turbulent Mixing Layer

The necessity for turbulent combustion modelling in the large-eddy simulation (LES) of premixed turbulent combustion is evident from the computational cost and the complexity of handling ame kinetics reaction mechanisms directly. In this paper a new ame-wrinkling LES combustion model using conditional ltering is proposed. The model represents an alternative approach to the traditional ame surface density based models in that the ame distribution is represented by a ame-wrinkle density function, and that the eeects of ame stretch and curvature are handled through a modelled transport equation for the perturbed laminar ame 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 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 prooles of velocity and its uctuations, temperature and reaction products. Good agreement is obtained, to a large extent due to accurate modelling of the ame wrinkle density, but also to the novel treatment of the strain-rate eeects on the laminar ame speed of the lean propane-air mixture.