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

Advanced Identification of Coherent Structures in Swirl-Stabilized Combustors

[+] Author and Article Information
Moritz Sieber

Chair of Fluid Dynamics
Technische Universität Berlin,
Müller-Breslau-Street 8,
Berlin 10623, Germany
e-mail: moritz.sieber@tu-berlin.de

Christian Oliver Paschereit, Kilian Oberleithner

Chair of Fluid Dynamics
Technische Universität Berlin,
Müller-Breslau-Street 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 June 20, 2016; final manuscript received June 21, 2016; published online September 13, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 139(2), 021503 (Sep 13, 2016) (8 pages) Paper No: GTP-16-1246; doi: 10.1115/1.4034261 History: Received June 20, 2016; Revised June 21, 2016

We present an application of a newly introduced method to analyze the time-resolved experimental data from the flow field of a swirl-stabilized combustor. This method is based on the classic proper orthogonal decomposition (POD) extended by a temporal constraint. The filter operation embedded in this method allows for continuous fading from the classic POD to the Fourier mode decomposition. This new method—called spectral proper orthogonal decomposition (SPOD)—allows for a clearer separation of the dominant mechanisms due to a clean spectral separation of phenomena. In this paper, the fundamentals of SPOD are shortly introduced. The actual focus is put on the application to a combustor flow. We analyze high-speed particle image velocimetry (PIV) measurements from flow fields in a combustor at different operation conditions. In these measurements, we consider externally actuated, as well as natural dynamics and reveal how the natural and actuated modes interact with each other. As shown in the paper, SPOD provides detailed insight into coherent structures in the swirl flames. Two distinct PVC structures are found that are very differently affected by acoustic actuation. The coherent structures are related to the heat release fluctuations, which are derived from simultaneously acquired OH* chemiluminescence measurements. Besides the actuated modes, a low frequency mode was found that significantly contribute to the global heat release fluctuations.

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Fig. 1

Sketch of the atmospheric combustion test-rig and measurement instrumentation

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Fig. 2

Natural mean velocity field (magnitude and streamlines)

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Fig. 3

Natural mean OH*-chemiluminescence field (de-Abeled) with superimposed streamlines

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Fig. 4

Relation between the sign of the crosswise velocities and the mode symmetries

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Fig. 5

POD (Nf = 0) modes of the natural flow

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Fig. 6

SPOD (Nf = 24) modes of the natural flow

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Fig. 7

SPOD spectrum (left) and spatial modes with mode coefficient spectrum (right) for increasing forcing amplitudes (from top to bottom the forcing amplitudes are 0, 10, 40, and 70% of the bulk velocity)

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Fig. 8

SPOD velocity modes Φi and the corresponding SPOD OH* modes Ωi for the dominant coherent structures

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Fig. 9

Time curve of the SPOD coefficient (ai) and the global heat release fluctuations (q′/q¯)

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Fig. 10

SPOD velocity modes Φi and corresponding SPOD OH* modes Ωi for the shift mode




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