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Research Papers

Heat Transfer in Reacting Cooling Films: Influence and Validation of Combustion Modeling in Numerical Simulations

[+] Author and Article Information
Stephanie Pohl

Institut für Thermodynamik,
Fakultät für Luft- und Raumfahrttechnik,
Universität der Bundeswehr München,
Werner-Heisenberg-Weg 39,
Neubiberg 85577, Germany
e-mail: stephanie.pohl@unibw.de

Gabriele Frank

Institut für Thermodynamik,
Fakultät für Luft- und Raumfahrttechnik,
Universität der Bundeswehr München,
Werner-Heisenberg-Weg 39,
Neubiberg 85577, Germany
e-mail: gabriele.frank@unibw.de

Michael Pfitzner

Institut für Thermodynamik,
Fakultät für Luft- und Raumfahrttechnik,
Universität der Bundeswehr München,
Werner-Heisenberg-Weg 39,
Neubiberg 85577, Germany
e-mail: michael.pfitzner@unibw.de

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received November 2, 2014; final manuscript received November 18, 2014; published online January 28, 2015. Editor: Kenneth C. Hall.

J. Turbomach 137(8), 081003 (Aug 01, 2015) (10 pages) Paper No: TURBO-14-1284; doi: 10.1115/1.4029350 History: Received November 02, 2014; Revised November 18, 2014; Online January 28, 2015

The demand for increased performance and lower weight of gas turbines gives rise to higher fuel-to-air ratios and a more compact design of the combustion chamber, thereby increasing the potential of fuel escaping unburnt from the combustor. Chemical reactions are likely to occur when the coolant air, used to protect the turbine blades, interacts with the unreacted fuel. Within this work, Reynolds-averaged Navier–Stokes (RANS) simulations of reacting cooling films exposed to high temperature fuel-rich exhaust gases are performed using the commercial computational fluid dynamics (CFD) code ansys fluent and validated against experimental results obtained at the Air Force Research Laboratory in Ohio. The results underline that the choice of the turbulence model has a significant impact on the evolution of the flow field and the mixing effectiveness. The flamelet as well as the equilibrium combustion model is able to predict an adequate distance of the reaction zone normal to the wall. Its thickness, however, is still much smaller and its onset too far upstream as compared to the experimental results. According to the present analysis, the flamelet combustion model applied along with k–ω shear stress transport (SST) or k–ε turbulence model turned out to be an appropriate choice in order to model near wall reacting flows with reasonable prospect of success.

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References

Figures

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Fig. 1

Cooling hole geometry taken from Ref. [7]

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Fig. 2

Computational domain and boundary conditions

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Fig. 3

Comparison of midplane temperature profile for different meshes: (a) 1.1 million cells (baseline mesh) and (b) 3 million cells (refined mesh)

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Fig. 4

Comparison of temperature profile for different meshes and axial locations

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Fig. 5

Detail of the mesh used for the numerical simulations

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Fig. 6

Mean value of temperature as function of the mean mixture fraction variance: left χst˜ = 0.1 s-1 and right χst˜ = 181 s-1

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Fig. 7

Comparison of dimensionless temperature profile at the midplane for different turbulence models: (a) standard k-[ɛ], (b) realizable k-[ɛ], and (c) k-[ω] SST. Combustion: flamelet concept.

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Fig. 8

Lines of constant Z˜ colored by their variance Z"2˜. Top: kε and bottom: k–ω SST.

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Fig. 9

Comparison of dimensionless temperature profile at the midplane for different combustion models and k–ω SST turbulence model. Left: air injection, right: N2 injection. (a) and (b) equilibrium model, (c) and (d) FR/ED model, and (e) and (f) flamelet model.

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Fig. 10

Distribution of scalar dissipation rate for k–ω SST turbulence model and flamelet combustion concept

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Fig. 11

Mixing effectiveness η⋆ for the use of different turbulence and combustion models

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Fig. 12

Simulated OH ⋆ molar concentration at midplane for equilibrium assumption (left) and chemiluminescence reaction (right) compared to experimental data taken from Ref. [7]. (a) experimentally measured OH*, (b) and (c) equilibrium with k-ω SST turbulence model, (d) FR/EDM and thermal equilibrium assumption not evaluable due to abscence of OH in 2-step mechanism, (e) FR/EDM with k-ω SST turbulence model (chemiluminuescence reaction), (f) and (g) flamelet with k-ω SST turbulence model (h) and (i) flamelet with k-ɛ turbulence model.

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