Modeling of premixed turbulent flames with second moment methods

Turbulent premixed flames feature complex interactions between turbulent transport of scalars and chemical reaction as well as a strong coupling between velocity and scalar turbulence. The present work concerns the modeling of such flames at the second moment closure level and mainly focuses on the critical role of pressure redistribution/scrambling. It is shown that the common and exclusive practice of past work in this area, which involves a density weighted rewriting of models derived on a constant density basis, is insufficient. To resolve this issue a class of model extensions is proposed to account for variable density effects. The accuracy of the proposed approach is illustrated by consideration of incompressible premixed turbulent flames in the laminar flamelet regime of combustion. However, the proposed approach is general and does not preclude the consideration of other combustion regimes or the use of sophisticated closures for reaction related terms. The full closure is here applied to the simulation of transient one-dimensional flames and fully two-dimensional flames stabilized in counterflow geometries. The obtained level of agreement with experimental data proves most encouraging and constitutes a significant advance over past modeling efforts. (C) 1998 by The Combustion Institute.