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

Flow Field and Flame Dynamics of Swirling Methane and Hydrogen Flames at Dry and Steam Diluted Conditions

[+] Author and Article Information
Steffen Terhaar

Chair of Fluid Dynamics
Hermann-Föttinger-Institut,
Technische Universität Berlin,
Müller-Breslau-Str. 8,
Berlin 10623, Germany
e-mail: steffen.terhaar@tu-berlin.de

Oliver Krüger, Christian Oliver Paschereit

Chair of Fluid Dynamics
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 July 14, 2014; final manuscript received July 24, 2014; published online October 28, 2014. Editor: David Wisler.

J. Eng. Gas Turbines Power 137(4), 041503 (Oct 28, 2014) (10 pages) Paper No: GTP-14-1391; doi: 10.1115/1.4028392 History: Received July 14, 2014; Revised July 24, 2014

The majority of recent stationary gas turbine combustors employ swirling flows for flame stabilization. The swirling flow undergoes vortex breakdown (VB) and exhibits a complex flow field including zones of recirculating fluid and regions of high shear intensities. Often, self-excited helical flow instabilities, which manifest in a precession of the vortex core, are found in these flows and may influence the combustion process in beneficial and adverse ways. In the present study, we investigate the occurrence and shape of self-excited hydrodynamic instabilities and their impact on heat release fluctuations and mixing characteristics over a wide range of operating conditions. We employ high-speed stereoscopic particle image velocimetry (S-PIV) and simultaneous OH*-chemiluminescence imaging to resolve the flow velocities and heat release distribution, respectively. The results reveal four different flame shapes: A detached annular flame, a long trumpet shaped flame, a V flame, and a very short flame anchored near the combustor inlet. The flame shapes were found to closely correlate with the reactivity of the mixture. Highly steam-diluted or very lean flames cause a detachment, whereas hydrogen fuel leads to very short flames. The detached flames feature a helical instability, which, in terms of frequency and shape, is similar to the isothermal case. A complete suppression of the helical structure is found for the V flame. Both the trumpet shaped flame and the very short flame feature helical instabilities of different frequencies and appearances. The phase-averaged OH*-chemiluminescence images show that the helical instabilities cause large-scale heat release fluctuations. The helical structure of the fluctuations is exploited to use a tomographic reconstruction technique. Furthermore, it is shown that the helical instability significantly enhances the mixing between the emanating jet and the central recirculation zone.

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References

Figures

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Fig. 1

Sketch of the combustor test-rig and the experimental setup

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Fig. 2

Initial jet opening angle over axial location of the flame for various operating conditions. The size of the marker indicates the rate of steam dilution and the color the mass fraction of hydrogen. Red squares show the selected operating conditions that are investigated in detail.

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Fig. 3

Initial jet opening angle over axial location of the flame for various operating conditions. The color of the marker indicates the calculated laminar flame speed.

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Fig. 4

Streamlines of the time-averaged flow fields and radial profiles of the axial (dashed lines 1.5 × u/u0) and tangential (solid lines 2 × w/u0) velocities superimposed on the normalized axial velocity distribution

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Fig. 5

Streamlines of the time-averaged flow fields and radial profiles of the estimated normalized density (solid lines ρ*) superimposed on the estimated normalized density distribution

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Fig. 6

Streamlines of the time-averaged flow fields superimposed on the normalized Abel-deconvoluted OH*-chemiluminescence intensity distribution. (a) Spectra and time traces of the POD time coefficients aj. (b) Spatial POD modes corresponding to the time traces shown in (a).

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Fig. 7

Results of the POD analysis for the detached flame. (a) Spectra and time traces of the POD time coefficients aj. (b) Spatial POD modes corresponding to the time traces shown in (a).

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Fig. 8

Results of the POD analysis for the V flame. (a) Spectra and time traces of the POD time coefficients aj. (b) Spatial POD modes corresponding to the time traces shown in (a).

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Fig. 9

Results of the POD analysis for the trumpet flame. (a) Spectra and time traces of the POD time coefficients aj. (b) Spatial POD modes corresponding to the time traces shown in (a).

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Fig. 10

Results of the POD analysis for the short hydrogen flame. (a) Spectra and time traces of the POD time coefficients aj. (b) Spatial POD modes corresponding to the time traces shown in (a).

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Fig. 11

Time trace of the estimated particle concentration at an arbitrarily chosen point in the region of burnt gases of the V flame. Red line represents the analytical fit (Eq. (4)) and the red circle indicates the estimated time-lag.

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Fig. 12

Normalized time-lag distribution: (a) isothermal, (b) V flame, (c) trumpet flame, (d) detached flame, and (e) short H2 flame

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Fig. 13

Phase-averaged OH*-chemiluminescence fluctuations of the detached flame at four different phase angles. Streamline of the time-averaged flow field are superimposed.

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Fig. 14

Reconstructed OH*-chemiluminescence fluctuations of the detached flame at four different phase angles. Streamline of the time-averaged flow field are superimposed.

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Fig. 15

Reconstructed OH*-chemiluminescence fluctuations of the trumpet flame at four different phase angles. Streamline of the time-averaged flow field are superimposed.

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Fig. 16

Reconstructed OH*-chemiluminescence fluctuations of the shorter hydrogen flame at four different phase angles. Streamline of the time-averaged flow field are superimposed.

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