Flame resolved simulation of a turbulent premixed bluff-body burner experiment. Part I: Analysis of the reaction zone dynamics with tabulated chemistry
Résumé
Results from a highly resolved simulation are presented for a turbulent lean premixed methane-air bluff body burner investigated experimentally at Cambridge University and Sandia National Laboratories. The Cartesian computational grid consists of 1.6 billion cells with a resolution of 100 mu m, which is sufficient to capture the laminar (thermal) flame thickness of 500 mu m. The combustion process is modeled with premixed flamelet generated manifolds (PFGM). The quality of the simulation is assessed by investigating the resolution of the flame- and velocity scales, it is demonstrated that the relevant scales are resolved in a direct numerical simulation (DNS) sense in the flame. The simulation is validated by comparing temporal statistics of velocity, temperature and major species mass fractions against experimental results. It is shown that the combustion regime varies with the distance from the burner and the progress of the reaction. Ensemble-averaged statistics, conditional means and averages along turbulent flamelets are compared against reference data from unstrained premixed one-dimensional flames. The analysis is carried out with respect to previous findings from DNS of much simpler flame configurations featuring synthetic turbulence. It is concluded that the major physical properties are comparable. In other words, most of the findings from previous DNS studies for canonical cases are relevant, at least for the lab scale jet-flame examined here. The flame normal strain is found to be aligned with the most compressive strain rate. The mean principal curvature of the progress variable iso-surfaces is predominantly zero and skewed towards positive values, the turbulent flame structure is mainly slightly thinned compared to the laminar one. The displacement speed of the flame is found to take partially negative values. The lack of correlation between the displacement speed and the consumption speed is also reported, the correlation being achieved considering the normal component of the diffusive flux only. (C) 2017 The Combustion Institute. Published by Elsevier Inc. All rights reserved.