| Large-eddy simulation is investigated in order to perform numerical simulations of turbulent combustion. Two problems are addressed in this work. First, the behavior of classical subgrid models for the transport of momentum and thermal energy under strong variation of density is studied. For this purpose, a heated turbulent plane jet with temperature variations of 8:1 and Rayleigh-Taylor turbulence with a density ratio of 3:1 are considered. Second, the subgrid modeling of scalar nonlinearities intrinsic to the combustion problem is analyzed, in particular one reconstruction procedure and one statistical approach.; Large-eddy simulations reproduce fairly accurately the large-scale behavior of the variable density flows considered here. Comparisons are made against available experimental and numerical data in terms of the general structure of the flow, expected values, spectra and probability-density functions.; With respect to the reconstruction subgrid models for nonlinear functions f (Z) studied here, results depend on the ratio of the subgrid variance of Z to the characteristic scale of the nonlinearity. If this ratio is sufficiently small, reconstruction approaches provide accurate predictions, better than an assumed density function. As the function becomes more and more local, the accuracy of the reconstruction model decreases (as expected) in favor of a mixed model in which the subgrid variance is provided by the reconstruction approach and the general nonlinearity is statistically modeled by an assumed density function. |
