Reduced description of reactive flows with tabulation of chemistry

Abstract

Abstract The direct use of large chemical mechanisms in multi-dimensional Computational Fluid Dynamics (CFD) is computationally expensive due to the large number of chemical species and the wide range of chemical time scales involved. To meet this challenge, a reduced description of reactive flows in combination with chemistry tabulation is proposed to effectively reduce the computational cost. In the reduced description, the species 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. When required, the unrepresented species are reconstructed assuming that they are in constrained chemical equilibrium. In situ adaptive tabulation (ISAT) is employed to speed the chemistry calculation through tabulating information of the reduced system. The proposed dimension-reduction / tabulation methodology determines and tabulates in situ the necessary information of the nr-dimensional reduced system based on the ns-species detailed mechanism. Compared to the full description with ISAT, the reduced descriptions achieve additional computational speed-up by solving fewer transport equations and faster ISAT retrieving. The approach is validated in both a methane/air premixed flame and a methane/air non-premixed flame. With the GRI 1.2 mechanism consisting of 31 species, the reduced descriptions (with 12 to 16 represented species) achieve a speed-up factor of up to three compared to the full description with ISAT, with a relatively moderate decrease in accuracy compared to the full description. Keywords: reduced description of reactive flowsdimension reductiontabulationconstrained equilibriumoperator splitting Acknowledgements Ren and Goldin are grateful to the financial support of the Austrian Kplus programme funded by the Federal Government of Austria as well as the State Governments of federal states of Styria and Lower Austria. The work at Cornell is funded in part by Department of Energy under Grant DE-FG02-90ER. SBP has a financial interest in Ithaca Combustion Enterprise, LLC, which has licensed the software ISAT-CK and CEQ used in this work.