Hybrid large-eddy simulation/Lagrangian filtered-density-function approach for simulating turbulent combustion

A consistent hybrid large-eddy simulation/filtered-density-function approach (LES-FDF) is formulated for variable-density low-Mach-number flows. The LES-FDF approach has been proposed as a suitable method for finite-rate-chemistry-based predictive modeling of turbulent reactive flows. Due to the large computational grid associated with LES, use of Lagrangian schemes is numerically expensive. In this work, a highly efficient parallel Lagrangian implementation is used for the simulation of a nonpremixed flame. This bluff-body-stabilized flame is characterized by complex flow fields that interact strongly with the combustion mechanism. A LES grid size of 1 million computational cells and roughly 15 million notional particles is used to simulate a time-accurate variable-density flow. The hybrid approach predicts the time-averaged velocity and root mean square (RMS) velocity components quite accurately. Species profiles including hydroxyl radical compare well with experimental data. Consistency and accuracy are established by comparing particle and Eulerian density, mixture fraction, and RMS mixture fraction fields. Scalar FDFs at select locations are shown to be well approximated by the presumed beta function used in typical combustion LES.