Lagrangian simulation of a thin non-premixed flame in the field of an asymmetric layer

Development of an analytical, subgrid-scale non-premixed combustion model for simulation of two-dimensional reacting shear flow at conditions of fast chemistry is described. The model is based on generalization of the classical one-dimensional flamelet representation to multi-dimensional flow conditions, and incorporation of resulting combustion model into adaptive, Lagrangian vortex element techniques. Evolution of the external flow field is computed by tracking the motion of vortex elements, while flame front topology is described by a collection of thin flamelets, which are also used to compute the unsteady response of the local flame structure to the prevailing strain. One of the interesting features of the model described herein is that, while maintaining computational efficiency, it does not oversimplify the flame structure and/or flow-field dynamics. In particular, all the essential features of flow-combustion interactions are retained, namely the effect of flow-induced stretch on the local flame structure and burning rates, and the impact of heat release on flow-field divergence and baroclinic vorticity generation. The efficiency of the numerical scheme is guaranteed by adaptively concentrating computational resources along the flame front and regions of finite vorticity. Implementation of the model is illustrated by computing the combustion field of a reacting layer in which the characteristic vorticity length scale is several orders of magnitude larger than the initial flame thickness.