Inflow Condition Effects on Large Eddy Simulations of Variable Density Mixing Layers

In this paper we present the results from a series of Large Eddy Simulations of the variable density plane turbulent mixing layer. Local Reynolds numbers, based on the velocity difference across the layer and its visual thickness, of up to 250,000 are achieved. The purpose of this study is to assess the effect of the nature of the inflow conditions on the vortex structure in the variable density mixing layer. A mixing layer originating from initially-laminar conditions with pseudo-random perturbations does not contain a spatially stationary streamwise vortex structure for any value of density ratio. Imposing physically-correlated fluctuations on the initially-laminar flow produces a mixing layer that does contain a spatially stationary structure for all density ratios. The evolution of this streamwise structure compares well with experimental observation. The asymptotic scaling of the streamwise structure wavelength to local vorticity thickness is independent of the density ratio, in agreement with previous experimental findings.