Simulations of a turbulent non-premixed flame using combined dimension reduction and tabulation for combustion chemistry

Abstract

The use of large chemical mechanisms of hydrocarbon fuels in turbulent flame simulations is computationally expensive due to the large number of chemical species and the wide range of chemical time scales involved. The reduced description of reactive flows in combination with chemistry tabulation can effectively reduce the simulation time when detailed chemical kinetics is employed in multi-dimensional Computational Fluid Dynamics (CFDs). In this study, this approach is applied to simulate a bluff-body-stabilized non-premixed flame with the eddy dissipation concept (EDC) and transported probability density function (PDF) combustion models. In the calculations, the 31 chemical species in the GRI-Mech 1.2 mechanism are partitioned into represented species and unrepresented species. The reactive system is described in terms of a smaller number of represented species instead of the full set of chemical species in the mechanism; and the evolution equations are solved only for the represented species. The In Situ Adaptive Tabulation (ISAT) approach is employed to speed the chemistry calculation by tabulating information of the reduced system. The simulations show that a reduced description with 13 represented species and three atomic elements in the unrepresented species agrees well with the full description that has 31 species while achieving a speed-up factor of up to three. Compared to experimental data, the PDF model yields more accurate predictions in the composition fields of upstream locations than EDC. The impact of the reduced description on NOx emissions is also studied by performing the full and reduced descriptions of the flame with GRI-Mech 3.0. The study shows that a reduced description with a total 16 represented species, including three nitrogen-containing species, agrees well with the full description and incurs less than 5% error in NO predictions. Moreover, in this study, an efficient initialization procedure is first demonstrated for the CFD calculations with detailed chemistry.