A low-dimensional stochastic closure model for combustion large-eddy simulation

Abstract

A novel formulation for the large-eddy simulation (LES) of turbulent combustion flows is presented. The formulation is based on coupling LES equations for mass and momentum, with the corresponding 1D stochastic governing equations using the One-Dimensional Turbulence (ODT) model. ODT domains, or elements, on which fine-grained ODT simulations are implemented, are embedded in the flow to represent unresolved scalar and momentum statistics. The formulation is designed to address important coupling between turbulent transport and molecular processes (reaction and diffusion) over a wide range of length and time scales. This coupling poses difficult challenges for the LES modeling of turbulent mixing and combustion flows. The LES-ODT approach is implemented for the problem of autoignition in non-homogeneous mixtures. The LES-ODT model yields excellent agreement with direct numerical simulations (DNS) of reactive scalars' statistics at different turbulence and Lewis number conditions. Comparisons of the LES-ODT results with DNS show that the model represents adequately turbulent transport through its filtered advection and stochastic stirring. Molecular transport exhibits important roles in determining the rate of heat and mass dissipation from the autoignition kernels and their propagation.