The performance of algebraic flame surface density (FSD) models has been assessed for flames with nonunity Lewis number (Le)\r\nin the thin reaction zones regime, using a direct numerical simulation (DNS) database of freely propagating turbulent premixed\r\nflames with Le ranging from 0.34 to 1.2. The focus is on algebraic FSD models based on a power-law approach, and the effects\r\nof Lewis number on the fractal dimension D and inner cut-off scale ?i have been studied in detail. It has been found that D is\r\nstrongly affected by Lewis number and increases significantly with decreasing Le. By contrast, ?i remains close to the laminar flame\r\nthermal thickness for all values of Le considered here. A parameterisation of D is proposed such that the effects of Lewis number\r\nare explicitly accounted for. The new parameterisation is used to propose a new algebraic model for FSD. The performance of the\r\nnew model is assessed with respect to results for the generalised FSD obtained from explicitly LES-filtered DNS data. It has been\r\nfound that the performance of the most existing models deteriorates with decreasing Lewis number, while the newly proposed\r\nmodel is found to perform as well or better than the most existing algebraic models for FSD.
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