Effects of combined dimension reduction and tabulation on the simulations of a turbulent premixed flame using a large-eddy simulation/probability density function method

Abstract

A turbulent lean-premixed propane–air flame stabilised by a triangular cylinder as a flame-holder is simulated to assess the accuracy and computational efficiency of combined dimension reduction and tabulation of chemistry. The computational condition matches the Volvo rig experiments. For the reactive simulation, the Lagrangian Large-Eddy Simulation/Probability Density Function (LES/PDF) formulation is used. A novel two-way coupling approach between LES and PDF is applied to obtain resolved density to reduce its statistical fluctuations. Composition mixing is evaluated by the modified Interaction-by-Exchange with the Mean (IEM) model. A baseline case uses In Situ Adaptive Tabulation (ISAT) to calculate chemical reactions efficiently. Its results demonstrate good agreement with the experimental measurements in turbulence statistics, temperature, and minor species mass fractions. For dimension reduction, 11 and 16 represented species are chosen and a variant of Rate Controlled Constrained Equilibrium (RCCE) is applied in conjunction with ISAT to each case. All the quantities in the comparison are indistinguishable from the baseline results using ISAT only. The combined use of RCCE/ISAT reduces the computational time for chemical reaction by more than 50%. However, for the current turbulent premixed flame, chemical reaction takes only a minor portion of the overall computational cost, in contrast to non-premixed flame simulations using LES/PDF, presumably due to the restricted manifold of purely premixed flame in the composition space. Instead, composition mixing is the major contributor to cost reduction since the mean-drift term, which is computationally expensive, is computed for the reduced representation. Overall, a reduction of more than 15% in the computational cost is obtained.

Keywords:

• LES/PDF simulation of turbulent premixed flame
• RCCE
• dimension reduction
• ISAT
• bluff-body stabilised flame

Acknowledgements

We are grateful to Dr P. Gokulakrishnan of Combustion Science & Engineering Inc. for providing the chemical mechanisms used in this work. We also gratefully acknowledge Caltech, the University of Colorado Bolder and Stanford University for licensing the NGA code used in this work. Any opinions, findings and conclusions, or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the United States Air Force.

Additional information

Funding

This work was supported by AFRL under SBIR-Topic AF093–162, and was performed in collaboration with Combustion Science & Engineering, Inc.This material is based upon work supported by the United States Air Force [Contract No. FA8650-11-C-2188].The computational resource was provided by the National Science Foundation through the Texas Advanced Computing Center [Grant No. TG-CTS090020].