Subgrid Simulations of Reacting Two-Phase Shear Layers*

A two-phase subgrid combustion model has been developed for large-eddy simulations (LES). 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 mixing than other LES closure techniques. In the present approach, the liquid droplets are tracked using the Lagrangian approach up to a pre-specified cut-off size. The phase change of the droplets both larger and smaller than the cut-off size and the subsequent mixing of the evaporated fuel with the oxidizer are modeled within the subgrid using an Eulerian two-phase model. It is shown here that the present approach gives consistently better results for both infinite and finite-rate kinetics in turbulent mixing layer even when the cut-off is increased. In contrast, conventional LES under similar conditions result in significant error when the cut-off size is increased. Finally, as a prelude to the study reacting sprays in realistic gas turbine combustors, a spatially evolving co-axial spray configuration is simulated using a new parallel LES version of the present model. Results are analyzed and discussed to demonstrate the new capability that has been developed.