8th Aeroacoustics Conference 1983
DOI: 10.2514/6.1983-759
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Application of 3-signal coherence to core noise transmission

Abstract: Gmm' G uu' Gxx auto-spectra of variables m(t), u(t), and x(t), respectively A method for determining transfer functions CD across turbofan engine components and from the en-Gmn, Gmp , Gnp cross-spectra between variables de-Ln gine to the far-field is developed. The method is noted by subscripts 4; based on the 3-signal coherence technique used previously to obtain far-field core noise levels. This G uv' G uw , Gvw cross-spectra between variables demethod eliminates the bias error in transfer funcnoted by subsc… Show more

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Cited by 7 publications
(4 citation statements)
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“…The coherence of noise radiated at different angles from a randomly distributed noise source is a function of the ratio of the noise source coherence length and the acoustic wavelength (Rajaram 2007). Such angular coherence measurements have been used to decompose combustion/turbine ('core noise') and jet noise sources in jet engines (Krejsa 1983). Figure 19(a) plots the dependence of the coherence between the 45 • and 90 • microphone data upon frequency for Case 1.…”
Section: Source Characterization and Turbulent Flame Dynamicsmentioning
confidence: 99%
See 1 more Smart Citation
“…The coherence of noise radiated at different angles from a randomly distributed noise source is a function of the ratio of the noise source coherence length and the acoustic wavelength (Rajaram 2007). Such angular coherence measurements have been used to decompose combustion/turbine ('core noise') and jet noise sources in jet engines (Krejsa 1983). Figure 19(a) plots the dependence of the coherence between the 45 • and 90 • microphone data upon frequency for Case 1.…”
Section: Source Characterization and Turbulent Flame Dynamicsmentioning
confidence: 99%
“…The focus of this paper is on open, premixed flames (see Ihme, Pitsch & Bodony 2006or Tam et al 2005 for recent work on non-premixed flames) with a fixed composition, i.e. on the actual acoustic radiation from the flame itself, without the effects of enclosures, which lead to sound reflections, and entropy generated noise by the acceleration of temperature inhomogeneities through nozzles (Marble & Candel 1977;Muthukrishnan, Strahle & Neale 1978;Shivashankara 1978;Cumpsty 1979;Krejsa 1983). The heat release rate of a premixed flame with constant composition and flame speed is proportional to its surface area (Clavin & Siggia 1991) -fluctuations in fuel/air ratio due to imperfect mixing/acoustic pulsations (Cho & Lieuwen 2005), or stretch-induced flame speed variations (Wang et al 2009), can also lead to heat release oscillations, effects which are outside of the scope of this investigation.…”
Section: Introductionmentioning
confidence: 99%
“…7 Similar studies were made by Krejsa at the same period. 8 The principle of the data processing was explained by Chung. 9 It continues to be extended thanks to the progress in computers, 10,11 and a novel method based on the same bases was implemented in TEENI.…”
Section: Introductionmentioning
confidence: 99%
“…Since flight effects reduce jet noise more than combustor noise, combustor noise can be a significant contributor to aircraft in-flight noise but may be masked by jet noise under the corresponding static-engine test conditions. To overcome this obstacle, researchers [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] developed coherence techniques utilizing engine-internal, as well as far-field, measurements to identify the far-field combustor-noise component. Modal analyses [24][25][26][27][28][29] were also carried out to determine the source and propagation characteristics of combustor noise.…”
Section: Nasa Sti Program In Profi Lementioning
confidence: 99%