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

A Methodology for On the Fly Acoustic Characterization of the Feeding Line Impedances in a Turbulent Swirled Combustor

[+] Author and Article Information
A. Lamraoui1

 Laboratoire EM2C–École Centrale Paris–CNRS, Grande voie des vignes, 92295 Châtenay-Malabry, Franceammar.lamraoui@em2c.ecp.fr

F. Richecoeur, T. Schuller, S. Ducruix

 Laboratoire EM2C–École Centrale Paris–CNRS, Grande voie des vignes, 92295 Châtenay-Malabry, France

1

Corresponding author.

J. Eng. Gas Turbines Power 133(1), 011504 (Sep 17, 2010) (7 pages) doi:10.1115/1.4001987 History: Received April 09, 2010; Revised April 15, 2010; Published September 17, 2010; Online September 17, 2010

A methodology is proposed to determine on the fly the acoustic impedances at the boundaries of a combustor under operation and without the need for an external forcing device. The methodology is applied hereby to obtain the reflection coefficients of the air and fuel feeding lines supplying a swirled combustor operating in lean conditions and featuring an unstable regime. It is based on a three-microphone technique and uses the combustion roar noise inside the chamber to get estimates of the boundary impedances in the low frequency limit. Conditions under which this method yields reliable results for the reflection coefficient are examined, and a criterion based on the coherence between microphone signals is proposed to determine the frequency bandwidth for impedance reconstruction. The method also takes into account the flow Mach number in the supplying pipes, which can be non-negligible because of their reduced diameter. The technique is validated against data obtained in a dedicated impedance measurement setup equipped with a high-efficiency loudspeaker.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Combustor test rig composed, from left to right, of a rear air injection unit, two identical injection stages, and a square cross-section chamber. Microphones are mounted at different points of the apparatus.

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Figure 2

Schematic view of the experimental facility with feeding lines. Propane and air are injected through two opposite inlets in two successive stages. The supplying lines are equipped with IMDs (see Fig. 3) to characterize their impedance at different locations.

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Figure 3

IMD used to measure the acoustic reflection coefficient along the feeding lines

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Figure 4

Instantaneous power spectral density measured at different locations in the combustion chamber and along the feeding lines during one run for Φ=0.75 and α=15%

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Figure 5

Reflection coefficient of the air/fuel feeding lines at the flow controller outlet compared with the same quantities calculated at the premixer inlets. Measurements are carried out on the fly on the combustion test rig.

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Figure 6

The air mass flow controller is mounted on the ITHACA impedance test bench. Air flow and acoustic level correspond to the ones encountered in the combustor.

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Figure 7

Comparison between reflection coefficients measured at the exit of the flow controller during a hot fire test and on the ITHACA test bench. Top to bottom: air from stage 1, fuel from stage 1, and fuel from stage 2.

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Figure 8

Coherence between the microphones A and C in the IMD during on the fly measurement

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Figure 9

Locations of the acoustic reflection coefficient measurements on the combustion test rig

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Figure 10

The measured and reconstructed acoustic reflection coefficients of the first stage air feeding line at the premixer inlet

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