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Research Papers: Gas Turbines: Controls, Diagnostics, and Instrumentation

Measurements of Density Pulsations in the Outlet Nozzle of a Combustion Chamber by Rayleigh-Scattering Searching Entropy Waves

[+] Author and Article Information
Anne Rausch1

Department of Engine Acoustics, Institute of Propulsion Technology, German Aerospace Center, 10623 Berlin, Germanyanne.rausch@dlr.de

Andre Fischer, Andrea Gaertlein, Steffen Nitsch, Karsten Knobloch, Friedrich Bake

Department of Engine Acoustics, Institute of Propulsion Technology, German Aerospace Center, 10623 Berlin, Germany

Holger Konle

Institute of Fluid Mechanics, Technische Universität Berlin, 10623 Berlin, Germany

Ingo Röhle

Department of Turbine, Institute of Propulsion Technology, German Aerospace Center, 37073 Göttingen, Germany

1

Corresponding author.

J. Eng. Gas Turbines Power 133(3), 031601 (Nov 10, 2010) (9 pages) doi:10.1115/1.4002018 History: Received April 15, 2010; Revised May 06, 2010; Published November 10, 2010; Online November 10, 2010

The development of measurement techniques, which enable temporal and spatial highly resolved density investigations even in harsh environments, is essential. Rayleigh scattering is a noninvasive optical measurement technique permitting such investigations. A Rayleigh-scattering measurement system is set up, providing a new insight into fluid mechanical processes in turbomachines. In this paper, Rayleigh scattering is used for the detection of density oscillations in the optical accessible convergent-divergent outlet nozzle of a small scale combustion test rig at various power consumptions and equivalence ratios. Until now, this part of the combustion chamber is sparsely investigated due to the challenging measurement conditions. The temporal density oscillation inside the nozzle can be shown up to 4 kHz as well as its spatial distribution. Systematic errors of the setup are investigated. Spectra of pressure and density oscillations are compared. Measurements with nonreacting air flow are conducted to study flow induced density fluctuations. Entropy noise related correlations between density and pressure fluctuations are found. Therewith, the builtup Rayleigh-scattering system enables investigations of the presumed region of indirect noise generation.

Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Setup of the combustion test rig and sensors

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Figure 2

Comparison of sound pressure levels in combustion chamber and exhaust duct at 15 kW thermal power and equivalence ratio 1

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Figure 3

Setup of the optical system for Rayleigh-Scattering measurements: La, laser; S1/S2/S3/S4, system of mirrors to traverse the beam horizontal and vertical; Di, diode; L, lens; B, aperture; Bd, beam dump; D, outlet nozzle; V, vibrometer; E, EMCCD; and Pm1/Pm2, photomultipliers

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Figure 4

Spectra of acoustic oscillations, test rig oscillations, and density oscillations in the nozzle at 5 kW thermal power, 0.83 equivalence ratio, and Ma=0.17

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Figure 5

Spectra of the density oscillations in the nozzle and oscillations of parasitic light at 5 kW thermal power, 0.83 equivalence ratio, and Ma=0.17

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Figure 6

Mean density measured by Rayleigh-scattering compared with density computed from thermocouple and static pressure sensor data

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Figure 7

Linear spectra of density oscillation in the outlet nozzle versus Mach number and frequency

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Figure 8

Linear spectra of pressure oscillation in the combustion chamber versus Mach number and frequency

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Figure 9

Linear spectra of pressure oscillation in the exhaust duct versus Mach number and frequency

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Figure 10

Temporal oscillations of the spatial density distribution in the outlet nozzle at 15 kW thermal power, 1.0 equivalence ratio, and Ma=0.55

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Figure 11

Coherence of microphone signals in combustion chamber and exhaust duct versus Mach number

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Figure 12

Coherence of microphone signals in combustion chamber and density signal in outlet nozzle versus Mach number

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Figure 13

Coherence of density signal in outlet nozzle and microphone signal in exhaust duct versus Mach number

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Figure 14

Comparison of coherences of pressure signals and density signal at 15 kW thermal power, equivalence ratio 1, and Ma=0.55

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Figure 15

Comparison of coherences of pressure signals and density signal of the nonreacting air flow at Ma=0.56.

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