Effects of artificial flame front thickening on intermediate minor species prediction using the LES–FGM method

Abstract

Two stratified premixed Cambridge/Sandia flames SwB1 and SwB9 are modelled using the Flamelet-Generated Manifold in the context of Large-eddy Simulation. Two kinds of sub-grid closure models are adopted and systematically compared, that is, the Dynamically Thickened Flame (DTF) and the Presumed Probable Density Function (PPDF) models, in order to study the effects of artificial flame front thickening introduced by the DTF on the intermediate minor species prediction. It is found that the two methods lead to similar modelling of velocity, temperature, mixture fraction and major species (e.g. CH, O, CO and HO). However, the intermediate minor species CO and H can be over-predicted using the DTF model compared to the PPDF. A correction method proposed recently by Gruhlke et al. is validated in this work to improve the CO/H predictions of DTF. The corrected CO/H mass fractions are nearly consistent with the results of PPDF. It is examined that the Gruhlke-correction performs better if the wrinkling factor is used directly without modification. Meanwhile, the correction exhibits similar good performance with different level of flame front thickening and mixture stratification. The correction is also addressed to correct the species only in the flame front. The results are significant in high-fidelity simulation of intermediate species using the DTF model.