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

# Influence of Transversal Acoustic Excitation of the Burner Approach Flow on the Flame Structure

[+] Author and Article Information
Martin Hauser1

Lehrstuhl für Thermodynamik, Technische Universität München, Boltzmannstraße 15, D-85748 Garching, Germanyhauser@td.mw.tum.de

Manuel Lorenz, Thomas Sattelmayer

Lehrstuhl für Thermodynamik, Technische Universität München, Boltzmannstraße 15, D-85748 Garching, Germany

1

Corresponding author.

J. Eng. Gas Turbines Power 133(4), 041501 (Nov 23, 2010) (8 pages) doi:10.1115/1.4002175 History: Received May 11, 2010; Revised May 12, 2010; Published November 23, 2010; Online November 23, 2010

## Abstract

Modern large gas turbines for power generation have multiple burners, which are distributed around the circumference of the engine and which generate flames in combustors of either annular or can-annular geometry. In both cases, considering only the axial modes has proven to be insufficient for the assessment of the thermoacoustic stability. An adequate analysis requires consideration of the circumferential acoustic coupling generated by the acoustic field in the upstream and downstream annuli and the open passages between the cans, respectively. As in annular combustors, the particularly critical eigenmodes with low frequencies are predominantly of circumferential nature; the stability of annular combustors is often governed by the onset of circumferential acoustic oscillations. To determine the influence of these circumferential acoustic modes on the dynamic flame behavior, a new single burner test rig was developed. The unique acoustic properties of the test rig allow the exposure of a single swirl burner to a two-dimensional acoustic field that resembles the circumferential mode in an annular combustor. Measurements were performed for axial as well as transversal excitation of the burner and the combination of both. To investigate the dynamic flame structure, phase-resolved flame images have been evaluated in terms of amplitude and phase distribution. Under transversal excitation, the flame structure becomes highly asymmetrical. A region of higher $OH∗$ intensity is generated in the combustion chamber, which rotates with the excitation frequency. From phase-resolved particle image velocimetry (PIV) measurements of the isothermal flow, it is concluded that the transversal excitation modulates the swirl generation leading to an asymmetrical velocity distribution in the burner nozzle and the combustion chamber.

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## Figures

Figure 1

Flame images of the annular combustor with axial excitation (top) and circumferential excitation of the plenum chamber (bottom) (11)

Figure 2

Schematic setup and CAD-model of the single burner test rig with its main components

Figure 3

Swirl generator (top left), plenum chamber cross-section (top right), and cross-section of plenum and combustion chamber (bottom)

Figure 4

FEM analysis of the acoustic velocity distribution along the transversal duct (y-axis)

Figure 5

Post-processing of the phase-resolved flame images

Figure 6

Orientation and position of the applied measurement techniques

Figure 7

Amplitude and weighted phase plots for axial excitation with 110 Hz (N)

Figure 8

Phase-resolved flame images for transversal excitation with 110 Hz (P: top and N: bottom)

Figure 9

Amplitude and weighted phase plots for transversal excitation with 110 Hz (N)

Figure 10

Amplitude and weighted phase plots for transversal excitation with 110 Hz (P)

Figure 11

Amplitude and weighted phase plots for transversal excitation with 150 Hz (N)

Figure 12

Phase-resolved velocity fields for isothermal flow in the combustion chamber under transversal excitation with 150 Hz (N)

Figure 13

Phase-resolved flame images for simultaneous excitation with 110 Hz (P: top and N: bottom)

Figure 14

Amplitude and weighted phase plots for simultaneous excitation with 110 Hz (P)

Figure 15

Amplitude and weighted phase plots for simultaneous excitation with 110 Hz (N)

Figure 16

Movement of the FSC for three different excitation scenarios with 110 Hz (N)

Figure 17

Axial intensity distribution of average flame images for the stationary case and three different excitation scenarios with 150 Hz

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