Flame Surface Density.

Burn Ing

I have a question regarding combustion modelling. In the Tabor and Weller paper "LES of premixed turbulent combustion using flame surface wrinkling model", Flow, turbulence and combustion, 72: 1-28, 2004 is the wrinking factor in effect the ratio of the total subgrid surface area divided by the surface area? This is as stated in the paper. Why is it that the source term in the reaction progress variable that contains the flame surface denity always talks about the sub-grid surface area? What about the filter level surface area? The source term seems to contain the effect of both filter level and subgrid flame surface area. Is all of the surface assumed to be within the small (sub grid ) scales? Any ideas or comments which can shed light on this would be of interest.