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Numerical simulations of Lewis number effects in turbulent premixed flames

Published online by Cambridge University Press:  26 April 2006

D. C. Haworth
Affiliation:
Thermosciences Department. General Motors Research Laboratories. Warren. MI 48090, USA
T. J. Poinsot
Affiliation:
Center for Turbulence Research, Stanford University, Stanford, CA 94305, USA Present address: Laboratoire EM2C, CNRS, Ecole Centrale de Paris, 92295 Chatenay-Malabry, Cedex, France.

Abstract

The structure of a premixed flame front propagating in a region of two-dimensional turbulence is investigated using full numerical simulation including heat release, variable properties, and one-step Arrhenius chemistry. The influence of reactant Lewis number (Le = ratio of thermal to species diffusivity) is reported for Le = 0.8, Le = 1.0, and Le = 1.2 flames. Local flame behaviour is described by comparing the local instantaneous turbulent flame structure (local consumption rate of reactants) to the steady one-dimensional laminar flame structure for the same thermochemical parameters. Statistics of flame front strain rates and curvature are calculated and global quantities of interest in modelling (flame surface area, mean reactant consumption rate per unit area of flame, and turbulent flame speed) are reported. Principal findings are: that probability density functions (p.d.f.s) of flame curvature are nearly symmetric about a near-zero mean; that the flame tends to align preferentially with extensive tangential strain rates; that the local flame structure of the non-unity Lewis number flames correlates more strongly with local flame curvature than with tangential strain rate; that the mean consumption rate per unit area is relatively insensitive to curvature and is controlled by the mean tangential strain rate; and, that more flame area is generated for Le < 1 than for Le > 1. Implications of the results for flamelet models of turbulent premixed combustion are discussed.

Type
Research Article
Copyright
© 1992 Cambridge University Press

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