LES/FDF of Turbulent Flames Using Complex Chemical Kinetics

Large eddy simulations (LES) of turbulent bluffbody and swirling flames, performed for the first time in conjunction with the filtered density function (FDF) model and complex chemical kinetics, are presented. The FDF model is a comprehensive turbulent-combustion model that directly computes the joint probability density function (PDF) of scalars and is therefore considered to be more accurate than conventional assumed-PDF type models. The simulations presented in the paper are performed using a C1 skeletal kinetics mechanism involving 16 species and 41 reaction steps. The complex mechanism allows prediction of major as well as minor species. Owing to the complexity of the mechanism, numerical integration of the kinetics equations is performed using the in situ adaptive tabulation (ISAT) scheme. LES of a bluffbody hydrogen-methane flame, a swirling methane flame and a swirling methane-air flame are presented in this study. Mean and RMS of velocity fields and mixture fraction, and means of temperature and species (major and minor) are presented and compared to data. Results indicate that velocities are predicted reasonably well in all the flames. The species and flame structures in the bluffbody flame and swirling methane-air flame are also predicted well. However, some deficiencies are seen in the computed flame structure of the swirling methane flame. These deficiencies may likely be overcome by using more sophisticated mixing models such as the Euclidean minimum spanning tree (EMST) model and chemical mechanisms involving higher hydrocarbons (C2 and above species). Discrepancies are also seen in the measured data in the swirling methane flame that need to be investigated further. Overall, the simulations represent the application of some of the most sophisticated LES submodels to the study of turbulent flames.