LES Model Assessment for High Speed Combustion using Mesh-Sequenced Realizations

Abstract

This work presents several simple models for accounting for the effects of unresolved fluctuations on filtered chemical production rates as used in large-eddy simulations with finite-rate chemistry. Modified a priori analyses, involving simultaneous fineand coarsemesh large-eddy simulations, are used to discover and evaluate candidate forms for an ‘enhancement factor’ that multiplies chemical production terms calculated according to the ‘laminar chemistry’ assumption and the law of mass action. The ‘enhancement factor’ is designed to account for mesh-scale effects on apparent reactivity. The models tested include variations of a scale-similarity approach based on least squares minimization and a partiallystirred reactor (PaSR) approach. The models work very well when velocity coupling is employed to connect the coarse-mesh realization to the simultaneous fine-mesh realization. Without velocity-coupling, the models do reduce local reactivity, relative to ‘laminar chemistry’, but improvements gained are modest and are confined to the ignition / stabilization regions.