Core Noise Diagnostics of Turbofan Engine Noise Using Correlation and Coherence Functions

Miles, J. H.

doi:10.2514/6.2009-1237

Cited by 5 publications

(8 citation statements)

References 37 publications

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“…7 and the total sound power calculations shown in Fig. 9 suggest the presence of indirect combustion noise at low frequencies due to the interaction of hot spots with the turbine and are similar to the results discussed by Miles [27][28][29] obtained using a smaller Honeywell TECH977 turbofan engine. The results obtained in the study of the smaller turbofan engine were identified using the convection time delay associated with the flow velocity of the entropy in the combustor.…”

Section: Three Signal Coherence Calculated Using Far-field Microphonessupporting

confidence: 72%

“…This shows the presence of combustion noise. Results from a study of noise from a smaller Honeywell TECH977 dual-spool turbofan engine by Miles [27][28][29] suggest this noise is due to an indirect combustion noise source.…”

Section: B Three Signal Coherence Techniquementioning

confidence: 99%

“…The smaller engine test results are reported in papers by Miles discussing a direct and indirect combustion noise source separation research program. [27][28][29] The core noise results discussed herein will be interpreted in terms of these more recent results.…”

mentioning

confidence: 99%

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Estimation of signal coherence threshold and concealed spectral lines applied to detection of turbofan engine combustion noise

Miles

2011

The Journal of the Acoustical Society of America

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Combustion noise from turbofan engines has become important, as the noise from sources like the fan and jet are reduced. An aligned and un-aligned coherence technique has been developed to determine a threshold level for the coherence and thereby help to separate the coherent combustion noise source from other noise sources measured with far-field microphones. This method is compared with a statistics based coherence threshold estimation method. In addition, the un-aligned coherence procedure at the same time also reveals periodicities, spectral lines, and undamped sinusoids hidden by broadband turbofan engine noise. In calculating the coherence threshold using a statistical method, one may use either the number of independent records or a larger number corresponding to the number of overlapped records used to create the average. Using data from a turbofan engine and a simulation this paper shows that applying the Fisher z-transform to the un-aligned coherence can aid in making the proper selection of samples and produce a reasonable statistics based coherence threshold. Examples are presented showing that the underlying tonal and coherent broad band structure which is buried under random broadband noise and jet noise can be determined. The method also shows the possible presence of indirect combustion noise.

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Section: Three Signal Coherence Calculated Using Far-field Microphonessupporting

confidence: 72%

Section: B Three Signal Coherence Techniquementioning

confidence: 99%

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Estimation of signal coherence threshold and concealed spectral lines applied to detection of turbofan engine combustion noise

Miles

2011

The Journal of the Acoustical Society of America

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“…8 show the correlation coefficients in the time region from 3.4 10 −3 s to 3.8 10 −3 s, which contains the peak value. As Miles (2006Miles ( , 2009) recently demonstrated, the correlation coefficient's peak region in a near-to far-field crosscorrelation is representative of different cause-effect and effecteffect mechanisms. The left side of the peak is determined by the direct correlated noise, which dominates the considered source and moves at acoustic speed along its full path to the far-field probe.…”

Section: Datum Aerofoilmentioning

confidence: 99%

“…The left side of the peak is determined by the direct correlated noise, which dominates the considered source and moves at acoustic speed along its full path to the far-field probe. (Miles (2009) dealt with the combustor pressure correlated noise in jet engines). The indirect aerodynamic noise controls the right side of the peak, which initially propagates with the mean flow velocity.…”

Section: Datum Aerofoilmentioning

confidence: 99%

Experimental study on the self-noise of a turbulent round jet investing a cambered aerofoil

Bianchi¹,

Corsini²,

Sheard

2013

Per. Pol. Mech. Eng.

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Spatial correlation in the ambient core noise field of a turbofan engine

Miles

2012

The Journal of the Acoustical Society of America

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An acoustic transfer function relating combustion noise and turbine exit noise in the presence of enclosed ambient core noise is investigated using a dynamic system model and an acoustic system model for the particular turbofan engine studied and for a range of operating conditions. Measurements of cross-spectra magnitude and phase between the combustor and turbine exit and auto-spectra at the turbine exit and combustor are used to show the presence of indirect and direct combustion noise over the frequency range of 0-400 Hz. The procedure used evaluates the ratio of direct to indirect combustion noise. The procedure used also evaluates the post-combustion residence time in the combustor which is a factor in the formation of thermal NO(x) and soot in this region. These measurements are masked by the ambient core noise sound field in this frequency range which is observable since the transducers are situated within an acoustic wavelength of one another. An ambient core noise field model based on one and two dimensional spatial correlation functions is used to replicate the spatially correlated response of the pair of transducers. The spatial correlation function increases measured attenuation due to destructive interference and masks the true attenuation of the turbine.

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Core Noise Diagnostics of Turbofan Engine Noise Using Correlation and Coherence Functions

Cited by 5 publications

References 37 publications

Estimation of signal coherence threshold and concealed spectral lines applied to detection of turbofan engine combustion noise

Estimation of signal coherence threshold and concealed spectral lines applied to detection of turbofan engine combustion noise

Experimental study on the self-noise of a turbulent round jet investing a cambered aerofoil

Spatial correlation in the ambient core noise field of a turbofan engine

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