Analysis of Shear Effects on Mixing and Reaction Layers in Premixed Turbulent Stratified Flames using LES coupled to Tabulated Chemistry

Abstract

ABSTRACT In this work, the effect of shear on turbulent lean premixed flames under stratified burning conditions including the flame TSF-A-r and TSF-D-r of the Darmstadt stratified burner, respectively, is numerically investigated. For this purpose, the large eddy simulation (LES) technique, coupled with tabulated chemistry and an artificially thickening approach, is applied. First, numerical predictions of time averaged data are compared with available experimental data in order to establish the prediction capability of the numerical approach. Then, the simulation results are exploited to analyze and characterize the stratified mixing layers and their interaction with the flame. In particular, coherent patterns in the mixing layers and their influence on the flame are pointed out. Finally, the onset and intensity of stratification of the two test cases are evaluated and compared in terms of equivalence ratio gradient, strength of the mixing and reaction layers, and scalar dissipation rates. It turns out that (1) a higher shear tends to attenuate the level of stratification, (2) the mixing and reaction layers correlate earlier and stronger with increasing turbulence, (3) a dominant premixed mode can rather be promoted with a stronger turbulence as can be observed from the ratio of the dissipation rate of the mixture fraction and that of the reaction progress variable.