Algebraic Closure of Scalar Dissipation Rate for Large Eddy Simulations of Turbulent Premixed Combustion

Abstract

An a-priori analysis of the filtered reaction rate closure based on Favre-filtered scalar dissipation rate (SDR) for large eddy simulations (LES) of turbulent premixed combustion has been conducted using a direct numerical simulation (DNS) database of freely propagating statistically planar flames for a range of different values of heat release parameter τ, global Lewis number Le, and turbulent Reynolds number Ret. It has been found that an existing SDR based reaction rate closure for Reynolds averaged Navier–Stokes (RANS) simulations is also valid for LES, when the filter width is larger than the flame thickness. This RANS-based reaction rate closure has been extended here for LES, and a satisfactory performance of this LES closure is observed for the values of filter widths, τ, Le, and Ret investigated here. A-priori DNS assessment of the SDR closures based on passive scalar mixing model and a power-law has been conducted. Moreover, an existing algebraic model of Favre-averaged SDR for RANS simulations has been extended here for LES. The performances of the algebraic closures of have been assessed with respect to Favre-filtered SDR extracted from the DNS data. It has been found that the newly proposed model for , which was extended here for LES from an existing RANS-based closure, predicts both local and volume-averaged behaviors of SDR satisfactorily for a range of for flames with different values of τ, Le, and Ret. The sensitivity of sub-grid turbulent velocity fluctuation modeling on the newly developed algebraic SDR closure has also been analyzed and it has been observed that the modeling does not significantly affect the performance of the algebraic SDR model proposed in this study.