LES of Subsonic Reacting Mixing Layers

We study a class of chemically reacting, spatially evolving, subsonic mixing layers via large eddy simulations (LES). A primary goal is to assess the inflow conditions, numerical methods, and physical models requirement to reproduce experimental results on molecular mixing and effects of inflow conditions in high-Reynolds number mixing layers: here, we target experiments performed by Slessor et al. (J. Fluid Mech. 376, 115-138 1998). The streams forming the mixing layer carry small amounts of hydrogen and fluorine, initiating a hypergolic reaction upon mixing at large Damkohler number. In this regime, product formation and temperature rise in the flow is mixing limited. The chemical compositions considered for this study correspond to low levels of heat release and results in adiabatic flame temperature rise of 171K and 267K. Both reacting and non-reacting simulations are performed with the Vreman sub-grid scale model (Vreman Phys. Fluids 16(10), 3670-3681 2004). A grid resolution study is done and comparisons are made with the available experimental data. To mitigate dispersive errors and ensure boundedness in species mass fractions that occur in simulations of non-premixed combustion, non-linear scaling limiters are used for reconstructing species densities during flux evaluation. The simulations show good agreement of the velocity and temperature rise profiles with experiment, and reveal differences in the flow field attributed to changes in the inflow conditions.