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

Amplitude-Dependent Flow Field and Flame Response to Axial and Tangential Velocity Fluctuations

[+] Author and Article Information
Sebastian Schimek

Hermann-Föttinger-Institut,
Technische Universität Berlin,
Müller-Breslau-Str. 8,
Berlin 10623, Germany
e-mail: Schimek@tu-berlin.de

Bernhard Ćosić, Jonas P. Moeck, Steffen Terhaar, Christian Oliver Paschereit

Hermann-Föttinger-Institut,
Technische Universität Berlin,
Müller-Breslau-Str. 8,
Berlin 10623, Germany

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 September 3, 2014; final manuscript received October 9, 2014; published online January 28, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 137(8), 081501 (Aug 01, 2015) (10 pages) Paper No: GTP-14-1525; doi: 10.1115/1.4029368 History: Received September 03, 2014; Revised October 09, 2014; Online January 28, 2015

The current paper investigates the nonlinear interaction of the flow field and the unsteady heat release rate and the role of swirl fluctuations. The test rig consists of a generic swirl-stabilized combustor fed with natural gas and equipped with a high-amplitude forcing device. The influence of the phase between axial and azimuthal velocity oscillations is assessed on the basis of the amplitude and phase relations between the velocity fluctuations at the inlet and the outlet of the burner. These relations are determined in the experiment with the multimicrophone-method and a two component laser Doppler velocimeter (LDV). Particle image velocimetry (PIV) and OH*-chemiluminescence measurements are conducted to study the interaction between the flow field and the flame. For several frequency regimes, characteristic properties of the forced flow field and flame are identified, and a strong amplitude dependence is observed. It is found that the convective time delay between the swirl generator and the flame has an important influence on swirl-number oscillations and the flame dynamics in the low-frequency regime. For mid and high frequencies, significant changes in the mean flow field and the mean flame position are identified for high forcing amplitudes. These affect the interaction between coherent structures and the flame and are suggested to be responsible for the saturation in the flame response at high forcing amplitudes.

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References

Figures

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Fig. 1

Acoustic energy balance and supercritical instability

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Fig. 2

Test rig overview with measurement devices

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Fig. 3

Burner, swirl generator with annular duct, and area jump to silica glass combustion chamber; flame angle (FA) and center of mass (COM) are indicated

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Fig. 4

Burner, cut through the movable block swirl generator

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Fig. 5

Acoustic burner describing function, gain, and phase of the transfer function relating axial velocity fluctuations at the swirler inlet to axial velocity fluctuations at the combustion chamber inlet. Symbols indicate the forcing level in terms of the normalized acoustic velocity amplitude (|u'|/u¯) at the combustion chamber inlet.

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Fig. 6

Acoustic burner describing function, gain, and phase of the transfer function relating axial velocity fluctuations at the swirler inlet to azimuthal velocity fluctuations at the combustion chamber inlet. Symbols indicate the forcing level in terms of the normalized acoustic velocity amplitude (|u'|/u¯) at the combustion chamber inlet.

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Fig. 7

Flame describing function for various forcing amplitudes. Symbols indicate the forcing level in terms of the normalized acoustic velocity amplitude (|u'|/u¯) at the combustion chamber inlet.

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Fig. 8

Two columns corresponding to u'/u¯ = 0.22 (left) and 0.33 (right) at 53 Hz. Each row corresponds to one of eight equidistant phases of the forcing period. Each individual picture shows the OH* image of the flame and the corresponding phase-averaged flow field.

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Fig. 9

Amplitude-dependent flame response at 53 Hz

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Fig. 10

Axial displacement of the COM of the OH*-chemiluminescence images versus acoustic displacement in the annular jet; straight line indicates equal acoustic and com displacements

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Fig. 11

Two columns corresponding to |u'|/u¯ = 0.19 (left) and 0.77 (right) at 123 Hz. Each row corresponds to one of eight equidistant phases of the forcing period. Each individual picture shows the OH* image of the flame and the corresponding phase-averaged flow field.

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Fig. 12

Amplitude-dependent flame response at 123 Hz

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Fig. 13

Two columns corresponding to |u'|/u¯ = 0.12 (left) and 0.75 (right) at 254 Hz. Each row corresponds to one of eight equidistant phases of the forcing period. Each individual picture shows the OH* image of the flame and the corresponding phase-averaged flow field.

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Fig. 14

Amplitude-dependent flame response at 254 Hz

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Fig. 15

FA at various forcing amplitudes at 254 Hz (black) and for various other forcing frequencies (gray)

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Fig. 16

Average over the oscillation cycle of the transverse moment of inertia of the phase-averaged OH* chemiluminescence distribution plotted against the acoustic displacement. Axial expansion of the flame increases with increasing forcing amplitude.

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Fig. 17

Two columns corresponding to |u'|/u¯ = 0.07 (left) and 0.37 (right) at 400 Hz. Each row corresponds to one of eight equidistant phases of the forcing period. Each individual picture shows the OH* image of the flame and the corresponding phase-averaged flow field.

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Fig. 18

Amplitude-dependent flame response at 400 Hz

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Fig. 19

Left: OH* image averaged over all phases; right: fluctuating part of OH* image at an arbitrary phase illustrating the convective length scale

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