Variable Density Effects in Stochastic Lagrangian Models for Turbulent Combustion
Cornell University Ithaca United States
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PDF methods have proven useful in modelling turbulent combustion, primarily because convection and complex reactions can be treated without the need for turbulence-modelling approximations. Xu and Pope 14,16 and Tang et al. 17 provide recent examples of such model calculations based on the modelled transport equation fir the joint PDF of velocity, turbulent frequency and composition species mass fractions and enthalpy. The advantages of PDF methods in dealing with chemical reaction and convection are preserved irrespective of density variation. Since the density variation in a typical combustion process may be as large as factor of seven, including variable-density effects in PDF methods is of significance. Conventionally, the strategy of modelling variable density flows in PDF methods is similar to that used for second-moment closure models SMCM models are developed based on a constant-density formulation, and then the same models are used for variable-density flows, but with density-weighted statistics in place of Reynolds averages.