LARGE EDDY SIMULATION OF A PREMIXED BUNSEN FLAME USING A MODIFIED THICKENED-FLAME MODEL AT TWO REYNOLDS NUMBER

摘要

A modified thickened flame (TF) model based on large eddy simulation (LES) methodology is used to investigate premixed combustion, and the model predictions are evaluated by comparing with the piloted premixed stoichiometric methane-air flame data for Reynolds numbers Re = 24,000 (flame F3) and Re = 52,000 (flame F1). The basic idea of the TF approach is that the flame front is artificially thickened to resolve on the computational LES grid while keeping the laminar flame speed (s_L~0) constant. The artificially thickening of the flame front is obtained by enhancing the molecular diffusion and decreasing the pre-exponential factor of the Arrhenius law. Because the flame front is artificially thickened, the response of the thickened flame to turbulence is affected and taken care of by incorporating an efficiency function (E) in the governing equations. The efficiency function (E) in the modified TF model is proposed based on the direct numerical simulations (DNS) data set of flame-vortex interactions. The predicted simulation results are compared with the experimental data and with computations reported using a Reynolds averaged Navier-Stokes (RANS)-based probability distribution function (PDF) modeling approach and RANS-based G-equation approach. It is shown that the results with the modified TF model are generally in good agreement with the data, with the TF predictions consistently comparable to the PDF model predictions and superior to the results with the G-equation approach.