The turbulent flame stretch accounts for the increase of flame surface area due to stretching and wrinkling of the flame front under turbulence. For the Extended Coherent Flame Model this effect is described by the Intermittent Turbulent Net Flame Stretch (ITNFS) model proposed by Meneveau and Poinsot [186]:

(7–80)

where is the laminar flame speed, is the laminar flame thickness, is the mean turbulent velocity fluctuation and is the integral length scale of turbulence, and,