The Use of Dynamic Adaptive Chemistry and Tabulation in Reactive Flow Simulations

Detailed chemical kinetics is an integral component for predictive simulation of turbulent flames and is important for reliable prediction of flames and emissions. Major challenges of incorporation of detailed chemistry in flame simulations are induced by the large number of chemical species and the wide range of timescales involved in detailed kinetics. In this work, dynamic adaptive chemistry (DAC) and in situ adaptive tabulation (ISAT) for efficient chemistry calculations in calculating turbulent reactive flows with detailed chemistry are studied in iso-octane/air homogeneous charge compression ignition (HCCI) and methane/air combustion in a partially-stirred reactor (PaSR). Chemistry calculations are accelerated by DAC via expediting the integration of ordinary differential equations (ODEs) governing chemical kinetics with local skeletal mechanisms obtained on-the-fly using the directed relation graph (DRG) method, and by ISAT via reducing the number of ODE integrations through tabulating and re-using the ODE solutions. It is shown that, in contrast to ISAT, the performance of DAC is mostly independent of the nature of combustion simulations, e.g., steady or unsteady, premixed or non-premixed combustion, and its efficiency increases with the size of chemical kinetic mechanisms. DAC is particularly suitable for transient combustion simulations with large mechanisms containing hundreds of species or more, such as those for gasoline or diesel fuels. A speedup factor of about 30 is achieved for HCCI combustion of iso-octane/air with good agreements in the histories of temperature and species concentrations. In contrast, ISAT performs better for simulations where chemistry calculations can be predominantly resolved by retrieving from the ISAT table, i.e., re-using the ODE solutions. It is shown that ISAT achieves speedup factors of about 100 with only about 10%, 0.1% and 0.01% incurred errors in NO, CO, and temperature, respectively, for the premixed methane/air PaSR simulations. Moreover, a combined DAC and ISAT approach, namely ISAT-DAC, has been developed and demonstrated in this study to accelerate chemistry evaluation. It is shown that the incurred errors in temperature and species concentrations in ISAT-DAC are well controlled, and it can significantly enhance the performance of ISAT, when the fraction of direct ODE integration is significant, via accelerating the ODE integrations by DAC.