A Priory Study of a Flamelet/Progress-Variable Approach for Non-premixed Turbulent Combustion

摘要

Large eddy simulation (LES) appears to be a promising approach for the numerical modeling of non-premixed, turbulent combustion processes. In this approach, unclosed chemical source terms appear in the filtered equations for species mass fractions and the temperature, which require modeling. Pierce and Moin have proposed a Flamelet/Progress-Variable approach, where a filtered equation for a progress variable is solved. The chemical source term is closed using a presumed probability density function (PDF) for the mixture fraction and progress variable. For the evaluation of the filtered chemical source term, in addition to the amelet assumption, it is assumed that mixture fraction and progress variable are uncorrelated, that the PDF of the progress variable is given by a δ-function, and that the PDF of the mixture fraction is given by a β-function. To assess further modeling needs, in the present study we test these individual assumptions using the direct numerical simulation (DNS) database by Sripakagorn et al. In these simulations, non-premixed combustion in isotropic decaying turbulence is considered, employing a one-step, global reversible reaction.