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

A Comparative Computational Fluid Dynamics Study on Flamelet-Generated Manifold and Steady Laminar Flamelet Modeling for Turbulent Flames

[+] Author and Article Information
Pravin Nakod

Senior Technology Specialist
34/1, Rajiv Gandhi Infotech Park,
Pune 411057, India
e-mail: pravin.nakod@ansys.com

Rakesh Yadav

Lead Software Developer
34/1, Rajiv Gandhi Infotech Park,
Pune 411057, India
e-mail: rakesh.yadav@ansys.com

Pravin Rajeshirke

Engineer, Support and Services
34/1, Rajiv Gandhi Infotech Park,
Pune 411057, India
e-mail: pravin.rajeshirke@ansys.com

Stefano Orsino

Technical Services Manager
10 Cavendish Court,
Centerra Resource Park,
Lebanon, NH 03766
e-mail: stefano.orsino@ansys.com

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received January 21, 2014; final manuscript received January 29, 2014; published online March 11, 2014. Editor: David Wisler.

J. Eng. Gas Turbines Power 136(8), 081504 (Mar 11, 2014) (8 pages) Paper No: GTP-14-1039; doi: 10.1115/1.4026806 History: Received January 21, 2014; Revised January 29, 2014

The laminar flamelet model (LFM) (Peters, 1986, “Laminar Diffusion Flamelet Models in Non-Premixed Combustion,” Prog. Energy Combust. Sci., 10, pp. 319–339; Peters, “Laminar Flamelet Concepts in Turbulent Combustion,” Proc. Combust. Inst., 21, pp. 1231–1250) represents the turbulent flame brush using statistical averaging of laminar flamelets whose structure is not affected by turbulence. The chemical nonequilibrium effects considered in this model are due to local turbulent straining only. In contrast, the flamelet-generated manifold (FGM) (van Oijen and de Goey, 2000, “Modeling of Premixed Laminar Flames Using Flamelet-Generated Manifolds,” Combust. Sci. Technol., 161, pp. 113–137) model considers that the scalar evolution; the realized trajectories on the thermochemical manifold in a turbulent flame are approximated by the scalar evolution similar to that in a laminar flame. This model does not involve any assumption on flame structure. Therefore, it can be successfully used to model ignition, slow chemistry, and quenching effects far away from the equilibrium. In FGM, 1D premixed flamelets are solved in reaction-progress space rather than physical space. This helps better solution convergence for the flamelets over the entire mixture fraction range, especially with large kinetic mechanisms at the flammability limits (ANSYS FLUENT 14.5 Theory Guide Help Document, http://www.ansys.com). In the present work, a systematic comparative study of the FGM model with the LFM for four different turbulent diffusion/premixed flames is presented. The first flame considered in this work is methane-air flame with dilution air at the downstream. The second and third flames considered are jet flames in a coaxial flow of hot combustion products from a lean premixed flame called Cabra lifted H2 and CH4 flames (Cabra, et al., 2002, “Simultaneous Laser Raman-Rayleigh-LIF Measurements and Numerical Modeling Results of a Lifted Turbulent H2/N2 Jet Flame in a Vitiated Coflow,” Proc. Combust. Inst., 29(2), pp. 1881–1888; Lifted CH4/Air Jet Flame in a Vitiated Coflow, http://www.me.berkeley.edu/cal/vcb/data/VCMAData.html) where the reacting flow associated with the central jet exhibits similar chemical kinetics, heat transfer, and molecular transport as recirculation burners without the complex recirculating fluid mechanics. The fourth flame considered is a Sandia flame D (Barlow et al., 2005, “Piloted Methane/Air Jet Flames: Scalar Structure and Transport Effects,” Combust. Flame, 143, pp. 433–449), a piloted methane-air jet flame. It is observed that the simulation results predicted by the FGM model are more physical and accurate compared to the LFM in all the flames presented in this work. The autoignition-controlled flame lift-off is also captured well in the cases of lifted flames using the FGM model.

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Fig. 1

2D axisymmetric geometry for test case 1

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Fig. 2

Cabra lifted hydrogen flame

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Fig. 4

Contours of progress variable and methane mass fraction for test case 1

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Fig. 5

Temperature and species mass fraction variation for Cabra lifted hydrogen flame

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Fig. 6

Temperature and species mass fraction variation for Cabra lifted methane flame

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Fig. 7

Axial velocity profiles in radial direction for Sandia flame D

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Fig. 8

Temperature and species mass fraction variation for Sandia flame D




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