RANS-SLFM and LES-SLFM numerical simulations of turbulent non-premixed oxy-fuel jet flames using CO2/O2 mixture
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Abstract
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
2 ( , , ) ZZ 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