An extended artificial thickening approach for strained premixed flames

Abstract

A method is presented to consistently treat artificial flame thickening in strained flows. Originally, the artificial thickened flame (ATF) approach was derived from a coordinate transformation for unstrained, freely propagating flames. Using the same transformation for a strained counterflow configuration, it is shown that global flame characteristics such as the consumption speed cannot be recovered. These observations, obtained using detailed and tabulated chemistry approaches, are then studied with an analysis of the deficiencies. Characteristic flame properties e.g. consumption speed and flame thickness, are compared, discussing the interplay of strain and flame thickening. The effect of strain on the individual budgets of the progress variable transport equation, including the spatial gradients, is then analyzed in composition space. Based on the findings, in the context of tabulated chemistry, a method is proposed to account for strain, reproducing the correct strain-dependent consumption speed while at the same time keeping the flame resolvable on coarse grids. The validity of this approach is finally demonstrated in 1D counterflow simulations with different strain rates and 2D Tsuji burner simulations with locally varying strain rates.