Modeling non-premixed laminar co-flow flames using flamelet-generated manifolds

The goal of this paper is to investigate the ability of the flamelet-generated manifold (FGM) approach for the numerical simulation of multidimensional laminar non-premixed flames. FGM’s constructed from premixed and non-premixed one-dimensional flamelets have been applied to a laminar methane flame in a co-flow of air. The results are compared to the solution of the full transport equations. Inclusion of differential diffusion with constant Lewis numbers for each species is studied. When unity-Lewis numbers are considered, an FGM which consists of counterflow diffusion flamelets is able to predict temperature and species concentrations in good agreement with the detailed solution (maximum difference ≈ 2%). Manifolds constructed from premixed flamelets show much larger deviations. Differential diffusion effects are hard to capture to a satisfactory level. Including non-unity Lewis numbers in solving the one-dimensional flamelets leads to improvement in the results, but using a simplified transport model for the progress variable YY in the application of the FGM, results in significant deviations. Large deviations, which are observed near the axis, are after an extensive analysis, attributed to an enhanced tangential diffusion effect due to curvature and stretch. These effects are not accounted for in the laminar counterflow diffusion flamelets. This is underlined by one-dimensional flamelet calculations. The results show the capability of FGM to reproduce planar flame structures with the inclusion of preferential diffusion by implementing a varying Lewis number for Y,LeY=f(Z,Y)Y,LeY=f(Z,Y).