A priori assessment of algebraic flame surface density models in the context of large eddy simulation for nonunity lewis number flames in the thin reaction zones regime
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jats:pThe performance of algebraic flame surface density (FSD) models has been assessed for flames with nonunity Lewis number (Le) in the thin reaction zones regime, using a direct numerical simulation (DNS) database of freely propagating turbulent premixed flames 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 of Lewis number on the fractal dimensionjats:italicD</jats:italic>and inner cut-off scale<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M1">mml:mrowmml:msubmml:miη</mml:mi>mml:mii</mml:mi></mml:msub></mml:mrow></mml:math>have been studied in detail. It has been found thatjats:italicD</jats:italic>is strongly affected by Lewis number and increases significantly with decreasing Le. By contrast,<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M2">mml:mrowmml:msubmml:miη</mml:mi>mml:mii</mml:mi></mml:msub></mml:mrow></mml:math>remains close to the laminar flame thermal thickness for all values of Le considered here. A parameterisation ofjats:italicD</jats:italic>is proposed such that the effects of Lewis number are explicitly accounted for. The new parameterisation is used to propose a new algebraic model for FSD. The performance of the new model is assessed with respect to results for the generalised FSD obtained from explicitly LES-filtered DNS data. It has been found that the performance of the most existing models deteriorates with decreasing Lewis number, while the newly proposed model is found to perform as well or better than the most existing algebraic models for FSD.</jats:p>
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2090-1976