| The focus of this work was to study the structure of multiple turbulent flame configurations using the steady laminar flamelet model (SLFM) coupled with Reynolds-averaged Navier-Stokes (RANS) and large eddy simulation (LES) transport equations. A detailed chemistry mechanism (GRI 3.0) was used in the formulation of the flamelet library. In addition, a probability density function (PDF) approach was used to generate the flamelet table in terms of its mean quantities &phis;(Z˜,Z˜"2, chi) as a function of the Favre-averaged mixture fraction, mixture fraction variance, and the scalar dissipation rate. A beta PDF was assumed for mixture fraction and a delta function distribution for the scalar dissipation rate. This approach ensured that finite-rate chemistry effects were introduced in the turbulent flow calculations. Radial mean and RMS distributions of temperature, mixture fraction, and species mass fractions were predicted at different axial locations for Sandia D and B-1 flames. The simulation results were validated against experimental data (Barlow & Frank 2007; Sevault et al. 2012). The validation study showed that LES/SFLM has better mean and RMS distributions for the B1 flame compared to RANS-SLFM. This was due to the fact that LES has a better representation of mixing than RANS since it resolves the large turbulent scales, which contain the largest amount of kinetic energy and control the mixing process in turbulent non-premixed combustion. Nonetheless, RANS-SLFM produced an acceptable mean profile for the Sandia D-flame for relatively low computational expense. However, mean radial profiles of minor species were not accurately predicted for either flame using RANS-SLFM, while good agreement was obtained with LES-SFLM. |
