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Research Papers: Gas Turbines: Aircraft Engine

Fundamental Mechanism of Entropy Noise in Aero-Engines: Experimental Investigation

[+] Author and Article Information
Friedrich Bake

Department of Engine Acoustics, Institute of Propulsion Technology, German Aerospace Center (DLR), Mueller-Breslau-Strasse 8, 10623 Berlin, Germanyfriedrich.bake@dlr.de

Nancy Kings, Ingo Roehle

Department of Engine Acoustics, Institute of Propulsion Technology, German Aerospace Center (DLR), Mueller-Breslau-Strasse 8, 10623 Berlin, Germany

J. Eng. Gas Turbines Power 130(1), 011202 (Jan 09, 2008) (6 pages) doi:10.1115/1.2749286 History: Received May 04, 2007; Revised May 07, 2007; Published January 09, 2008

Entropy noise caused by combustors increases rapidly with rising Mach number in the nozzle downstream of the combustion chamber. This is experimentally shown with a dedicated test facility, in which entropy waves are generated in a controlled way by unsteady electrical heating of fine platinum wires immersed in the flow. Downstream of the heating module called entropy wave generator (EWG), the pipe flow is accelerated through a convergent-divergent nozzle with a maximum Mach number of 1.2 downstream of the nozzle throat. Parameters like mass flux of the flow, nozzle Mach number, amount of heating energy, excitation mode (periodic, pulsed, or continuously), and propagation length between EWG and nozzle have been varied for the analysis of the generated entropy noise. The results are compared with the results of a one-dimensional theory found in early literature.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Sketch of the entropy wave generator (EWG); Tube section ΔXEWG-nozzle is variable, corresponding to different propagation lengths of entropy waves

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Figure 2

Photo of the entropy wave generator (EWG)

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Figure 3

Convecting entropy wave (solid red line) in terms of flow temperature perturbation measured by a fast thermocouple downstream of the heating module; the dotted black line shows the heating trigger signal

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Figure 4

Phase averaged time series of EWG microphone signals in the pulse excitation mode for different tube lengths Δx between heating module (EWG) and nozzle

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Figure 5

Phase averaged time series of entropy-wave-generator microphone signals in the pulse excitation mode at different bulk velocities

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Figure 6

Phase relation of cross spectra between heating current and microphone signals downstream of nozzle for different tube lengths between heating module (EWG) and nozzle

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Figure 7

Mach number distribution of the EWG nozzle flowfield; RANS simulation of reference test case

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Figure 8

Comparison of experimental data and results of the numerical simulation; acoustic pressure signal of microphone downstream of the nozzle

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Figure 9

Acoustic pressure pulse amplitude of generated entropy noise at different nozzle mach numbers and amplitudes of accelerated temperature or entropy perturbations

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Figure 10

Acoustic pressure pulse amplitude of generated entropy noise over accelerated temperature perturbation for two different nozzle Mach numbers Manozzle=0.15 and Manozzle=1

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Figure 11

Acoustic pressure pulse amplitude of generated entropy noise over nozzle Mach number for two different amplitudes of accelerated temperature perturbation

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Figure 12

Comparison of experimental data with theoretical prediction; normalized entropy sound pressure over nozzle Mach number

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