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

An Experimental Investigation of the Nonlinear Response of an Atmospheric Swirl-Stabilized Premixed Flame

[+] Author and Article Information
Sebastian Schimek1

Chair of Fluid Dynamics, Institute of Fluid Dynamics and Technical Acoustics, Hermann-Föttinger-Institut, Technische Universität Berlin, 10623 Berlin, Germanysebastian.schimek@pi.tu-berlin.de

Jonas P. Moeck, Christian Oliver Paschereit

Chair of Fluid Dynamics, Institute of Fluid Dynamics and Technical Acoustics, Hermann-Föttinger-Institut, Technische Universität Berlin, 10623 Berlin, Germany

1

Corresponding author.

J. Eng. Gas Turbines Power 133(10), 101502 (Apr 25, 2011) (7 pages) doi:10.1115/1.4002946 History: Received May 18, 2010; Revised May 27, 2010; Published April 25, 2011; Online April 25, 2011

Due to stringent emission restrictions, modern gas turbines mostly rely on lean premixed combustion. Since this combustion mode is susceptible to thermoacoustic instabilities, there is a need for modeling tools with predictive capabilities. Linear network models are able to predict the occurrence of thermoacoustic instabilities but yield no information on the oscillation amplitude. The prediction of the pulsation levels and hence an estimation whether a certain operating condition has to be avoided is only possible if information on the nonlinear flame response is available. Typically, the flame response shows saturation at high forcing amplitudes. A newly constructed atmospheric test rig, specifically designed for the realization of high excitation amplitudes over a broad frequency range, is used to generate extremely high acoustic forcing power with velocity fluctuations of up to 100% of the mean flow. The test rig consists of a generic combustor with a premixed swirl-stabilized natural gas flame, where the upstream part has a variable length to generate adaptive resonances of the acoustic field. The OH chemiluminescence response, with respect to velocity fluctuations at the burner, is measured for various excitation frequencies and amplitudes. From these measurements, an amplitude dependent flame transfer function is obtained. Phase-averaged OH pictures are used to identify changes in the flame shape related to saturation mechanisms. For different frequency regimes, different saturation mechanisms are identified.

Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Acoustic energy balance

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Figure 2

Test rig overview

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Figure 3

Burner, left: swirl generator with annular duct and area jump to silica glass combustion chamber; right: cut through the movable block swirl generator

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Figure 4

Principle sketch of pressure fluctuation due to flame response to sweep excitation; resonant frequencies are used for monofrequent excitation

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Figure 5

Sketch of the combustion chamber and image of the flame

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Figure 6

Flame describing function for u′/umean=0.1,0.2,0.3,0.4,0.5, arrow indicates increasing amplitudes

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Figure 7

OH∗ response at 128 Hz

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Figure 8

OH∗ pictures of the flame at a forcing frequency of 128 Hz: phase-averaged, Abel deconvoluted, for increasing excitation amplitudes

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Figure 9

OH∗ chemiluminescence intensity normalized with its mean value; averaged over the non-Abel deconvoluted flame images at 128 Hz for different forcing amplitudes; arrow indicates direction of increasing forcing amplitude

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Figure 10

Center of mass movement over one period at a forcing frequency of 128 Hz; arrow indicates direction of increasing forcing amplitude; saturation at four highest amplitudes visible; coordinates related to combustion chamber inlet

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Figure 11

Center of mass averaged over one period—each line for one frequency at different excitation amplitudes, starting at the squares

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Figure 12

OH∗ response at 292 Hz

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Figure 13

OH∗ pictures of the flame at a forcing frequency of 292 Hz: phase-averaged, Abel deconvoluted, for increasing excitation amplitudes

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Figure 14

OH∗ chemiluminescence intensity—for each excitation amplitude normalized with its mean value; averaged over the non-Abel deconvoluted flame images at 292 Hz; arrow indicates direction of increasing forcing amplitude

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Figure 15

Photomultiplier signal of a self-excited instability at 173 Hz

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Figure 16

Normalized OH∗ response at 159 Hz (top), 184 Hz (middle), and 50 Hz (bottom)

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