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For the premixed combustion component which will be solved at simulation runtime, the Zimont turbulent flame speed model includes the laminar flame speed (which determines the chemistry of the system) and the flame front evolution due to turbulence. The assumption to use this model is that the turbulence lengthscale in the flame is smaller than the flame thickness (Karlovitz number Ka > 1) where

{latex} $$
{Ka} = { (\nu \epsilon)^{1/4} \over (U_{laminar flame speed})^2}
$$
{latex}

Combining these two models is straightforward. The reaction progress variable c is used to track the location of the flame, called the flame front. Before (to the left of) the flame front at c=0, the mixture is unburnt, and the mass fractions and other variables are computed using mixture the precomputed mixture fraction PDFs. Inside the flame, a combination of the two models is used. In the burnt area (to the right of the flame at c=1), the equilibrium mixture fraction is computed.

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