A laminar flamelet approach to subgrid-scale chemistry in turbulent flows

A method is presented whereby filtered chemical species may be modeled in large eddy simulations (LES) of nonpremixed, turbulent combustion. The model is based an the concept of laminar flamelets, and assumes that a filtered mixture-fraction, as well as its subgrid-scale variance and filtered dissipation rate, are known at each grid cell of an LES. The model makes use of the subgrid-scale or ''large-eddy'' probability density function of the mixture-fraction, which is assumed to follow a beta-distribution. Also, an assumed functional form for the scalar dissipation rate is employed. The model is evaluated by filtering data from direct numerical simulations (DNS) of homogeneous, isotropic, decaying turbulence. Results show that the model, termed the large-eddy, laminar flamelet model (LELFM), is reasonably accurate and that the accuracy improves with increasing Damkohler number. (C) 1997 by The Combustion Institute.