Richardson, E.S., Sankaran, R., Grout, R.W. and Chen, J.H.
Numerical analysis of reaction-diffusion effects on species mixing rates in turbulent premixed methane-air combustion
Combustion and Flame, 157, (3), . (doi:10.1016/j.combustflame.2009.11.007).
The scalar mixing time scale, a key quantity in many turbulent combustion models, is investigated for reactive scalars in premixed combustion. Direct numerical simulations (DNS) of three-dimensional, turbulent Bunsen ?ames with reduced methane-air chemistry have been analyzed in the thin reaction zones regime. Previous conclusions from single step chemistry DNS studies are con?rmed regarding the role of dilatation and turbulence-chemistry interactions on the progress variable dissipation rate. Compared to the progress variable, the mixing rates of intermediate species is found to be several times greater. The variation of species mixing rates are explained with reference to the structure of one-dimensional premixed laminar ?ames. According to this analysis, mixing rates are governed by the strong gradients which are imposed by ?amelet structures at high Damk¨ohler numbers. This suggests a modeling approach to estimate the mixing rate of individual species which can be applied, for example, in transported probability density function simulations. Flame turbulence interactions which modify the ?amelet based representation are analyzed.
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