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Research Papers: Gas Turbines: Combustion, Fuels, and Emissions

Development and Validation of a Thickened Flame Modeling Approach for Large Eddy Simulation of Premixed Combustion

[+] Author and Article Information
Peter A. Strakey

National Energy Technology Laboratory, US DOE, Morgantown, WV 26507

Gilles Eggenspieler

 ANSYS Inc., Canonsburg, PA 15317

J. Eng. Gas Turbines Power 132(7), 071501 (Apr 07, 2010) (9 pages) doi:10.1115/1.4000119 History: Received April 08, 2009; Revised April 10, 2009; Published April 07, 2010; Online April 07, 2010

The development of a dynamic thickened flame (TF) turbulence-chemistry interaction model is presented based on a novel approach to determine the subfilter flame wrinkling efficiency. The basic premise of the TF model is to artificially decrease the reaction rates and increase the species and thermal diffusivities by the same amount, which thickens the flame to a scale that can be resolved on the large eddy simulation (LES) grid while still recovering the laminar flame speed. The TF modeling approach adopted here uses local reaction rates and gradients of product species to thicken the flame to a scale large enough to be resolved by the LES grid. The thickening factor, which is a function of the local grid size and laminar flame thickness, is only applied in the flame region and is commonly referred to as dynamic thickening. Spatial filtering of the velocity field is used to determine the efficiency function by accounting for turbulent kinetic energy between the grid-scale and the thickened flame scale. The TF model was implemented into the commercial computational fluid dynamics code FLUENT . Validation in the approach is conducted by comparing model results to experimental data collected in a laboratory-scale burner. The burner is based on an enclosed scaled-down version of the low swirl injector developed at Lawrence Berkeley National Laboratory. A perfectly premixed lean methane-air flame was studied, as well as the cold-flow characteristics of the combustor. Planar laser induced fluorescence of the hydroxyl molecule was collected for the combusting condition, as well as the velocity field data using particle image velocimetry. Thermal imaging of the quartz liner surface temperature was also conducted to validate the thermal wall boundary conditions applied in the LES calculations.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of flame and turbulence scales relative to the grid scale

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Figure 2

Schematic of burner geometry with inset photo of flame

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Figure 3

Contour plot of grid cell size (mm). Cutting plane through center of combustor.

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Figure 4

Radial profiles of mean axial velocity (left) and rms axial velocity (right) at axial locations of 1.5 mm, 5 mm, 10 mm, and 20 mm for the LES calculation and PIV data

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Figure 5

Radial profiles of rms fluctuating velocity and fluctuating velocity at the filter scale using Eq. 8 and the current filtering method from a cold-flow LES calculation

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Figure 6

Six snapshots of instantaneous OH fluorescence intensity, ϕ=0.7

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Figure 7

Measured velocity vectors colored by mean axial velocity overlaid with measured OH fluorescence intensity contours. Central contour at maximum OH intensity.

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Figure 8

Mean heat release from TF one-step, TF four-step, EBU one-step, laminar four-step simulations and experimentally derived average heat release

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Figure 9

Mean OH fluorescence (center) and mean OH concentration from laminar four-step (left) and TF four-step (right) LESs

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Figure 10

Radial plots of mean axial velocity for the four LES calculations along with the PIV data at axial locations of 1.5 mm, 5 mm, 10 mm, and 20 mm (top to bottom)

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Figure 11

Radial plots of rms axial velocity for the four LES calculations along with the PIV data at axial locations of 1.5 mm, 5 mm, 10 mm, and 20 mm (top to bottom)

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