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

High-Frequency Thermoacoustic Modulation Mechanisms in Swirl-Stabilized Gas Turbine Combustors—Part II: Modeling and Analysis

[+] Author and Article Information
Tobias Hummel

Lehrstuhl für Thermodynamik,
Technische Universität München,
Garching 85748, Germany;
Institute for Advanced Study,
Technische Universität München,
Garching 85748, Germany
e-mail: hummel@td.mw.tum.de

Frederik Berger

Lehrstuhl für Thermodynamik,
Technische Universität München,
Garching 85748, Germany
e-mail: berger@td.mw.tum.de

Michael Hertweck

Lehrstuhl für Thermodynamik,
Technische Universität München,
Garching 85748, Germany
e-mail: hertweck@td.mw.tum.de

Bruno Schuermans

Institute for Advanced Study,
Technische Universität München,
Garching 85748, Germany;
GE Power,
Baden 5401, Switzerland
e-mail: bruno.schuermans@ge.com

Thomas Sattelmayer

Lehrstuhl für Thermodynamik,
Technische Universität München,
Garching 85748, Germany
e-mail: sattelmayer@td.mw.tum.de

1Corresponding author.

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 11, 2016; final manuscript received November 30, 2016; published online February 14, 2017. Editor: David Wisler.

J. Eng. Gas Turbines Power 139(7), 071502 (Feb 14, 2017) (10 pages) Paper No: GTP-16-1324; doi: 10.1115/1.4035592 History: Received July 11, 2016; Revised November 30, 2016

This paper deals with high-frequency (HF) thermoacoustic instabilities in swirl-stabilized gas turbine combustors. Driving mechanisms associated with periodic flame displacement and flame shape deformations are theoretically discussed, and corresponding flame transfer functions (FTF) are derived from first principles. These linear feedback models are then evaluated by means of a lab-scale swirl-stabilized combustor in combination with part one of this joint publication. For this purpose, the models are used to thermoacoustically characterize a complete set of operation points of this combustor facility. Specifically, growth rates of the first transversal modes are computed, and compared against experimentally obtained pressure amplitudes as an indicator for thermoacoustic stability. The characterization is based on a hybrid analysis approach relying on a frequency domain formulation of acoustic conservation equations, in which nonuniform temperature fields and distributed thermoacoustic source terms/flame transfer functions can be straightforwardly considered. The relative contribution of flame displacement and deformation driving mechanisms–i.e., their significance with respect to the total driving–is identified. Furthermore, promoting/inhibiting conditions for the occurrence of high frequency, transversal acoustic instabilities within swirl-stabilized gas turbine combustors are revealed.

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References

Figures

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Fig. 1

Schematic of experimental combustor (dimensions in mm)

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Fig. 2

Illustration of flame displacement during one acoustic period Ta at four time instances of the oscillation cycle

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Fig. 3

Heat release fluctuations due to flame displacement

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Fig. 4

Heat release fluctuations due to flame shape deformation

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Fig. 5

Local oscillation of heat release and pressure

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Fig. 6

Sample mean heat release and temperature distribution

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Fig. 7

Mesh and boundary conditions

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Fig. 8

Comparison of numerical versus experimental oscillation frequencies of all considered operation point for validation purposes

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Fig. 9

Growth rates versus thermal power density

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Fig. 10

Growth rates versus oscillation amplitudes

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Fig. 11

Relative contributions to total driving

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Fig. 12

Intersection zone between pressure mode and flame contour

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