On aero-acoustic measurements in wind tunnels by means of a highly directional microphone system

Grosche, F.-R.; Stiewitt, H.; Binder, Bradley T.

doi:10.2514/6.1976-535

Cited by 7 publications

(3 citation statements)

References 4 publications

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“…In Fig. 5, a comparison between the theoretical predictions [57,93,94] assuming a Gaussian turbulence model and the measured coherence in the DNW-NWB open-jet wind tunnel [92] is shown. It can be seen that, as expected, the coherence loss increases with the freestream velocity, the sound frequency, and the streamwise distance of the microphone.…”

Section: Microphone Weighting and Coherence Lossmentioning

confidence: 99%

A review of acoustic imaging methods using phased microphone arrays

et al. 2019

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Phased microphone arrays have become a well-established tool for performing aeroacoustic measurements in wind tunnels (both open-jet and closed-section), flying aircraft, and engine test beds. This paper provides a review of the most wellknown and state-of-the-art acoustic imaging methods and recommendations on when to use them. Several exemplary results showing the performance of most methods in aeroacoustic applications are included. This manuscript provides a general introduction to aeroacoustic measurements for non-experienced microphone-array users as well as a broad overview for general aeroacoustic experts.

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Section: Microphone Weighting and Coherence Lossmentioning

confidence: 99%

A review of acoustic imaging methods using phased microphone arrays

et al. 2019

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“…Let P,-exp( -uot) denote the free-space pressure field due to a distribution of sources and let />exp(-uut) denote the pressure at the mirror microphone. Using Green's theoremandapplyingtheimpermeabilitycondition on the surface of the mirror, we can write -£-G(r m , r 0 ) (1) Here r m refers to the microphone location and r 0 to a point on the mirror surface. The free-space Green's function G is given by G(r m ,r 0 ) = e\p(ikR 0 J/(4nR 0m ), where R^ is the distance Ir 0 -r m \.…”

Section: Diffraction Model and Basic Mirror Propertiesmentioning

confidence: 99%

“…Directional dish-microphone systems gained popularity in aeroacoustics following the work of Grosche 1 and Kendall 2 in the 1970s. These authors demonstrated the possibility of mapping aeroacoustic noise sources with ellipsoidal and spheroidal dish-microphonesystems.…”

Section: Introductionmentioning

confidence: 99%

Interpretation of acoustic source maps made with an elliptic-mirror directional microphone system

Sen¹

1996

Aeroacoustics Conference

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Because of their directional properties, ellipsoidal dish-microphones (elliptic mirrors) have proved useful for locating noise sources in aeroacoustic flows. A scan of the source region produces a source map. It is customary to interpret a source map as a slightly blurred but otherwise faithful representation of the underlying source distribution. The spatial distribution of the sound pressure level is assumed to represent the main features of the layout and relative strengths of the sources. In this paper, we discuss a number of factors that introduce distortions or aberrations in the transformation from source strength distribution to source map. When aberrations are operative, a source map can convey misleading information about the source distribution. Some aberrations are related to test setup, and we show that these are fairly simple to avoid or correct for. However, a more fundamental distortion is induced by source spatial correlation or directivity. This is discussed using a discrete model of a source distribution. Finally, it is shown that for uncorrelated source clusters, aggregate source strength may be estimated by direct area-integration of a source map. (Author) Page 1 Downloaded by CORNELL UNIVERSITY on July 30, 2015 | http://arc.aiaa.org | Abstract Because of their directional properties, ellipsoidal dish-microphones (elliptic mirrors) have proved useful for locating noise sources in aeroacoustic flows. A scan of the source region produces a source map.It is customary to interpret a source map as a slightly blurred but otherwise faithful representation of the underlying source distribution: the spatial distribution of sound pressure level is assumed to represent the main features of the layout and relative strengths of the sources. In this paper, we discuss a number of factors that introduce distortions or aberrations in the transformation from source strength distribution to source map. When aberrations are operative, a source map can convey misleading information about the source distribution. Some aberrations are related to test setup, and we show that these are fairly simple to avoid or correct for. However, a more fundamental distortion is induced by source spatial correlation or directivity. This is discussed using a discrete model of a source distribution. Finally, it is shown that for uncorrelatedsourceclusters,aggregatesourcestrength may be estimated by direct area-integration of a source map.

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Investigation of Rotor Noise Source Mechanisms with Forward Speed Simulation

Grosche

Stiewitt

1978

AIAA Journal

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On aero-acoustic measurements in wind tunnels by means of a highly directional microphone system

Cited by 7 publications

References 4 publications

A review of acoustic imaging methods using phased microphone arrays

A review of acoustic imaging methods using phased microphone arrays

Interpretation of acoustic source maps made with an elliptic-mirror directional microphone system

Investigation of Rotor Noise Source Mechanisms with Forward Speed Simulation

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