Abstract
The LEM3D stochastic model for numerical simulation of turbulent mixing is used to simulate differential molecular diffusion effects in an isothermal jet of hydrogen and Freon 22 issued into air. The computations are compared with a published experimental study of the flow configuration. Salient features of the measured results are reproduced qualitatively, but the absence of spatial variation of the smallest eddy motion in LEM3D omits the streamwise variation of this length scale in the experimental configuration, resulting in a systematic deviation from the experimental trend. A first-principles basis for incorporating this missing physics into LEM3D is described, indicating the path forward for physically based quantitative prediction of differential diffusion effects, and turbulent combustion phenomenology more generally, using LEM3D.