Flame Surface Density based mean reaction rate closure for Reynolds averaged Navier Stokes methodology in turbulent premixed Bunsen flames with non-unity Lewis number

The Flame Surface Density (FSD) based mean reaction rate closure proposed by Prof. K.N.C. Bray and co-workers in the context of Reynolds Averaged Navier-Stokes simulations has been a-priori analysed using a Direct Numerical Simulation (DNS) database turbulent premixed Bunsen flames with different characteristic Lewis numbers representing strict flamelet regime (i.e. high Damköhler number low Karlovitz combustion). statistical behaviours stretch factor, orientation factor wrinkling length scale have assessed for non-unity conditions to identify their dependencies. assumption presumed bimodal distribution found be rendered invalid close nozzle exit where unresolved remains relatively small even when flow parameters at represent conditions. Although PDF progress variable shows some resemblance away from exit, Bray-Moss-Libby expressions which can derived infinitely large values show considerable deviations averaged variance extracted DNS data though these cases wrinkled/corrugated flamelets combustion on This suggests that it might necessary solve modelled scalar transport equation instead algebraic relation variance. It major influence scale, factor. Furthermore, are (sometimes strong) functions axial distance exit. Known parameterisations shown unable capture correct variation across flame brush analysis data. variability inadequacy existing relations approximate other quantities such as potential severely limit performance FSD closures within regime.