Hybrid presumed pdf and flame surface density approaches for Large-Eddy Simulation of premixed turbulent combustion: Part 1: Formalism and simulation of a quasi-steady burner

Abstract

Extended Coherent Flame Model for Large-Eddy Simulation (ECFM-LES) and Presumed Conditional Moments-Flame Prolongation of Intrisic Low Dimensional Manifolds (PCM-FPI) are some of the combustion models exploited for Large-Eddy Simulations (LES) of turbulent premixed flames. Combustion is then either modeled by tracking the flame surface density or by combining computations of flamelets with presumed probability density functions (pdf). The first approach enables to control the turbulent flame speed but models chemical kinetics in a simplified manner. The second directly accounts for detailed chemistry via the flamelet structure but the turbulent propagation speed cannot be easily estimated a priori. Simple one-dimensional tests are then performed in this study to evaluate flame velocities of PCM-FPI. A restricted operating range of this model, that enables to retrieve an evolution of the propagating speed similar to ECFM-LES predictions, is highlighted. This zone is limited in terms of filter width and sub-grid scale turbulent viscosity. An attractive alternative to both ECFM-LES and PCM-FPI approaches thus appears to be a model integrating their respective main strengths. For this purpose, two hybrid models are proposed in this paper and tested through LES of a lean-premixed turbulent swirling flame. Results in terms of statistics for temperature and mass fractions of chemical species are compared to experimental data and to previous results already obtained with PCM-FPI. The coupled models enable to properly locate the reaction zone via the flame surface density closures along with a correct prediction of the chemistry evolution in the flame front.