Imaging of Directional Distributed Noise Sources

Papamoschou, Dimitri

doi:10.2514/6.2008-2885

Cited by 21 publications

(31 citation statements)

References 22 publications

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“…The use of multiple microphones for noise source location goes back to the polar correlation method by Fisher et al [9] and the study of phased-array beamforming by Billingsley and Kinns [10]. Since then, phased arrays have found growing application in the detection of airframe noise [11,12] and jet noise [13][14][15]. Identification of the jet noise source is particularly challenging because it requires modeling of the noise source distribution [9].…”

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confidence: 99%

Beamformed Flow-Acoustic Correlations in a Supersonic Jet

2010

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An experimental study of simultaneous multipoint measurements in the flowfield and acoustic field of a Mach 1.75 cold-air jet is presented. A series of four optical-deflectometer probes measured turbulent fluctuations in or near the jet flow, and eight microphones recorded the far-field pressure in the direction of peak emission. The correlation methodology involves the coherence between the delay-and-sum beamformer outputs of the optical-deflectometer probes and the microphones. This procedure yields results with greater fidelity and higher coherence levels than obtained with individual optical-deflectometer-to-microphone correlations. With the optical-deflectometer probes in the jet shear layer, there is a significant correlation, on the order of 0.1, between the turbulent fluctuations and farfield noise. As the optical-deflectometer probe moves transversely away from the jet, its correlation with the microphone beamformer first drops and then increases. This trend signifies the transition from hydrodynamic to acoustic pressure fields. In the vicinity of the nozzle exit, the peak coherence between the beamformed opticaldeflectometer and microphone signals coincides with the physical location of the optical-deflectometer probe. However, as the shear layer thickens downstream, the peak coherence generally lags the probe location, which is a probable result of acoustic refraction by the mean flow.

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Beamformed Flow-Acoustic Correlations in a Supersonic Jet

2010

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“…Beamforming techniques provide the axial and frequency distribution of the noise sources for the valve. The deconvolution method of Papamoschou [1] was used for the noise source imaging.…”

Section: B Flow Facility and Diagnosticsmentioning

confidence: 99%

Noise Reduction of a Turbofan Bleed Valve

Phong

Nezhad

Liu

et al. 2012

50th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition

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A combined experimental and computational research effort investigated the noise sources of a pneumatic bleed valve used in turbofan engines and developed engineering solutions for attenuating those sources. The experimental effort employed 1/4-scale, rapid-prototyped valve designs which enabled the exploration of a large parameter space. Microphone array systems surveyed the sound and its sources, and Pitot surveys measured the mean velocity downstream of the valve. The numerical code solved the Reynolds-Averaged Navier Stokes (RANS) in both steady and unsteady modes. The research addressed the flow and acoustics of the valve without and with a muffler. The noise of the isolated valve consists of conventional jet noise with strong excess sound originating from the valve exit. The excess sound was traced to vortex shedding by support struts. Streamlining of the struts, aided by computational parametric studies, eliminated this noise component. The noise of the complete valve, with muffler attached, was attenuated by two principal means: using the streamlined struts and adding a honeycomb flow straightener to the muffler cavity. Proper installation of the honeycomb is critical for maximizing noise reduction. The resulting best design achieved a reduction of approximately 8 decibels in perceived noise level.

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“…5b). The method is based broadly on the DAMAS approach of Brooks and Humphreys 8 with additional features for self-consistent imaging of directional sources developed by Papamoschou 9 . Deconvolution utilized the Richardson-Lucy inversion method 9,10 .…”

Section: B Aeroacoustic Testingmentioning

confidence: 99%

Effects of Source Redistribution on Jet Noise Shielding

Mayoral

Papamoschou

2010

48th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition

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The potential of jet noise shielding from the Hybrid Wing Body (HWB) airplane is investigated in subscale experiments. The jet nozzle had a bypass ratio 10 and was operated at realistic takeoff exhaust conditions using helium-air mixtures. The shield, fabricated from a thin flat plate, had the generic shape of the HWB planform. Redistribution of the jet noise source is essential for achieving substantial noise reduction. Devices used to alter the jet noise source comprised chevrons (in mild and aggressive configurations) and a number of porous wedge fan flow deflectors. Using the estimated cumulative (downward plus sideline) EPNL reduction as a figure of merit, shielding of the plain nozzle yields a 2.4 dB reduction. Application of the aggressive chevrons increases the reduction to 6.5 dB, while the best wedge configuration improves this figure to 6.9 dB. Combination of wedge and aggressive chevrons yields a benefit of 7.6 dB. Examination of high-definition noise source maps shows a direct link between the insertion loss and the axial location of peak noise source. The aggressive chevrons cause an abrupt contraction of the noise source length at Strouhal number Sr=1.2, while the wedge induces a gradual contraction with increasing frequency. As a result, the insertion loss with the aggressive chevrons is stronger than with the wedge. However, because the wedge is inherently quieter than the chevrons, it gives a slightly better overall benefit. Surveys of the mean flow field show that the wedge, and its combination with chevrons, produces a significant reduction in the potential core length. On the other hand, the chevrons alone induce modest changes in the length of the high-speed region of the jet. Therefore, the mean velocity field by itself cannot provide useful information for inferring the noise source length for these complicated flows.

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Imaging of Directional Distributed Noise Sources

Cited by 21 publications

References 22 publications

Beamformed Flow-Acoustic Correlations in a Supersonic Jet

Beamformed Flow-Acoustic Correlations in a Supersonic Jet

Noise Reduction of a Turbofan Bleed Valve

Effects of Source Redistribution on Jet Noise Shielding

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