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

Large Eddy Simulation of Premixed Combustion With a Thickened-Flame Approach

[+] Author and Article Information
Ashoke De

Department of Mechanical Engineering, Louisiana State University, Baton Rouge, LA 70803

Sumanta Acharya1

Department of Mechanical Engineering and Turbine Innovation and Energy Research Center, Louisiana State University, Baton Rouge, LA 70803acharya@me.lsu.edu

See www.loni.org.

See www.hpc.lsu.edu.

1

Corresponding author.

J. Eng. Gas Turbines Power 131(6), 061501 (Jul 14, 2009) (11 pages) doi:10.1115/1.3094021 History: Received October 15, 2008; Revised October 17, 2008; Published July 14, 2009

A thickened-flame (TF) modeling approach is combined with a large eddy simulation (LES) methodology to model premixed combustion, and the accuracy of these model predictions is evaluated by comparing with the piloted premixed stoichiometric methane-air flame data of Chen (1996, “The Detailed Flame Structure of Highly Stretched Turbulent Premixed Methane-Air Flames  ,” Combust. Flame, 107, pp. 233–244) at a Reynolds number Re=24,000. In the TF model, the flame front is artificially thickened to resolve it on the computational LES grid and the reaction rates are specified using reduced chemistry. The response of the thickened-flame to turbulence is taken care of by incorporating an efficiency function in the governing equations. The efficiency function depends on the characteristics of the local turbulence and on the characteristics of the premixed flame such as laminar flame speed and thickness. Three variants of the TF model are examined: the original thickened-flame model, the power-law flame-wrinkling model, and the dynamically modified TF model. Reasonable agreement is found when comparing predictions with the experimental data and with computations reported using a probability distribution function modeling approach. The results of the TF model are in better agreement with data when compared with the predictions of the G-equation approach.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of the Bunsen burner with enlarge pilot flame (6)

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Figure 2

Instantaneous flow field. (a) Velocity (m/s) and (b) temperature (K).

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Figure 3

Cold flow: mean axial velocity U/Uo and turbulent kinetic energy k/Uo2×20. Experimental data are shown by symbols (△) and lines are LES results: coarse (—) and fine (- - - - -).

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Figure 4

Two-step chemistry (left) and one-step chemistry (right): mean axial velocity U/Uo (top) and turbulent kinetic energy k/Uo2 (bottom). Experimental data (△), Lindstedt simulations (●), Duchamp simulations (◼), TF model (—), power-law (- - - - -), dynamically modified TF model (−⋅−⋅−), and dynamically modified power-law model (—).

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Figure 5

Two-step chemistry (left) and one-step chemistry (right): mean temperature C. Legend—see Fig. 4.

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Figure 6

Reacting flow: mean axial velocity U/Uo. Experimental data (△), Lindstedt simulations (●), Duchamp simulations (◼), and TF model (—).

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Figure 7

Reacting flow: turbulent kinetic energy k/Uo2. Legend—see Fig. 6.

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Figure 8

Reacting flow: mean temperature C. Legend—see Fig. 6.

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Figure 9

Reacting flow: mean CH4 (△, ○, —), O2 (◻, ◇, — —), and H2O (▲, ●, −⋅−) concentrations. Experimental data (△, ◻, ▲), Lindstedt simulations (○, ◇, ●), and lines are TF model predictions.

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Figure 10

Reacting flow: mean CO×10 (△, ○, —) and CO2 (▲, ●, — —) concentrations. Experimental data (△, ▲), Lindstedt simulations (○, ●), and lines are TF model predictions.

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Figure 11

Turbulent flame-brush thickness lf,t: experimental data (△), Lindstedt simulations (○), Duchamp simulations (◼), and TF model (◇)

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