Investigation of aero-engine core-noise using a phased microphone array

Siller, H.; Arnold, F.; Deutschland, Rolls-Royce; Michel, U.

doi:10.2514/6.2001-2269

Cited by 15 publications

(14 citation statements)

References 5 publications

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“…Similar results were obtained by Miles (2006) 11 in the study of a Pratt & Whitney PW4098 turbofan engine, by Siller et al(2001) 12 in the study of core noise from a Rolls-Royce BR700 aeroengine, and in the study of an AVCO Lycoming YF-102 by Karchmer and Reshotko (1976), 1 and Karchmer (1977).…”

Section: Discussionsupporting

confidence: 71%

“…The effect of the jet on combustor coherence was noted by Muthukrshnam et al (1978) 10 in a test of a single fuel spray nozzle combustor assembly. A similar effect of the jet on the coherence function between a microphone array focused on the nozzle and a rumble probe is discussed for tests of a BR700 engine by Siller et al (2001). 12 Since much of the low-frequency noise appears to come from jet mixing at the end of the jet potential core, using acoustic liners in the turbofan nozzle exhaust system to remove core noise will not remove much low-frequency noise except at low engine speed settings where the jet noise is reduced.…”

Section: Discussionmentioning

confidence: 99%

“…Core noise of a Rolls-Royce BR700 aero-engine has also been studied with the aid of a phased linear array of microphones by Siller et al (2001) 12 and a combustor pressure sensor. Coherence between the combustor pressure sensor and a phased-array signal was obtained and the coherent array output power spectrum was measured.…”

Section: Introductionmentioning

confidence: 99%

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Spectral Separation of the Turbofan Engine Coherent Combustion Noise Component

Miles

2008

46th AIAA Aerospace Sciences Meeting and Exhibit

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Section: Discussionsupporting

confidence: 71%

Section: Discussionmentioning

confidence: 99%

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Spectral Separation of the Turbofan Engine Coherent Combustion Noise Component

Miles

2008

46th AIAA Aerospace Sciences Meeting and Exhibit

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“…This is the "linear" interpretation of the data presented in Siller et al . 11 Column three shows the same increase in power of the three linear terms as in column 1 but in this case, due to the non-linear nature of the quadratic term, it increases relatively more, causing it to dominate, which results in the drop in coherence. It is therefore the presence of the non-linearity that causes the drop in coherence and not a decrease in the combustion noise relative to the other linear terms.…”

Section: A Introductionmentioning

confidence: 90%

“…A drop in coherence between combustion noise measurements made at the combustor can with pressure transducers, and microphone array measurements focused on the exit plane of an aero-engine, when the rpm of the engine was increased, was reported by Siller et al . 11 An interpretation of this result is that, when the jet noise is low for low engine power settings, the core noise is a significant contributor to noise in the near-field. However, as the jet noise becomes more significant, the coherence drops due to the relatively low contribution of the combustion noise.…”

Section: A Introductionmentioning

confidence: 99%

Noise Source Identification for Ducted Fan Systems

Bennett

Fitzpatrick

2007

13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference)

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Understanding combustion noise source mechanisms, designing efficient acoustic liners and optimising active control algorithms for noise reduction requires the identification of the frequency and modal content of the combustion noise contribution. Coherence-based noise source identification techniques have been developed which can be used to identify the contribution of combustion noise to near and far-field acoustic measurements of aeroengines. A number of existing identification techniques from the literature are implemented and evaluated under controlled experimental conditions. An experimental rig was designed and built to gain a fundamental physical understanding of the convection of noise through a rotor/stator set-up. The identification techniques were applied to this rig and the pressure field was separated into its constituent parts.The underlying assumption with these identification techniques is that the propagation/convection path, from combustion can to measurement point, is a linear one. It is shown with simulations that where the combustion noise propagates in a non-linear fashion the identified contribution will be inaccurate. The experimental rig, consisting of a vaneaxial fan mounted in a duct, allows potential non-linear interaction mechanisms between a convected sound source and the fan to be investigated. Tests carried out on the experimental rig allowed a non-linear interaction tone, between the rotor BPF and a convected tone, to be generated.An experimental technique was developed which enabled the non-linear interaction between the convected sound source with the vane-axial fan to be detected and identified when present. The technique was extended to allow the linear and non-linear acoustic contributions to be separated. The capacity to decompose the coherent output power into linear and non-linear components is a useful tool for the correct design of acoustic treatment for core noise and for an accurate identification of noise source generating mechanisms.The non-linear identification techniques, developed with the experimental rig, were applied to data from full scale turbo-fan engine tests. A Rolls-Royce engine was instrumented with pressure transducers at the combustor can and in the hot-jet pipe, and microphones were placed in the near-field. For a particular power setting, frequency scattering was seen to occur between the combustion noise and the high pressure turbine which was measurable in the hot jet pipe after convection through the many turbine stages. The techniques allowed the non-linear interaction to be successfully identified and linear and non-linear coherent output powers to be determined. Nomenclature γ 2 ij Ordinary Coherence Function between signals i(t) and j(t) G ijAveraged single-sided power cross-spectral density between signals i(t) and j(t)

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