Subgrid Modeling of Unsteady Two-Phase Turbulent Flows*

A subgrid scalar mixing and combustion model originally developed for gas phase combustion has been extended in this study to include the liquid phase. This approach includes a more fundamental treatment of the effects of the final stages of droplet vaporization, molecular diffusion, chemical reactions and small scale turbulent stirring than other LES closure techniques. As a result, Reynolds, Schmidt and Damkohler number effects are explicitly included. This model has been implemented within an Eulerian-Lagrangian two phase large-eddy simulation (LES) formulation. In this approach, the liquid droplets are tracked using the Lagrangian approach up to a pre-specified cut-off size. The evaporation and mixing of the droplets smaller than the cutoff size is modeled within the subgrid using an Eulerian two-phase model that is an extension of the earlier gas-phase subgrid model. The issues related to the implementation of this subgrid model within the LES are discussed in this paper along with some preliminary results that demonstrate its capabilities.