Optimization of Microphone Array Wall Mountings in Closed-Section Wind Tunnels

Fleury, Vincent; Coste, Laurent; Davy, Renaud; Mignosi, A.; Cariou, Charles; Prosper, Jean-Marc

doi:10.2514/1.j051336

Cited by 33 publications

(17 citation statements)

References 10 publications

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“…However, it is advantageous to couple these signal processing techniques with actual reductions in the TBL fluctuations. A common approach to reducing TBL wall noise is by recessing the microphones in cavities and covering these cavities with a metallic mesh or Kevlar [5,9,10]. These approaches, coupled with array processing, can approximately reduce the measured background noise by an additional 10 dB for an array [5].…”

Section: Introductionmentioning

confidence: 99%

Design and Evaluation of Microphone Cavity Geometries for Wind-Tunnel Acoustic Measurements

VanDercreek

Majunath

Ragni

et al. 2019

AIAA Scitech 2019 Forum

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This study investigated how embedding microphones in different cavity geometries reduce the measured turbulent boundary layer pressure fluctuations at the microphones. The cavity geometries were systematically varied using a design of experiments (DOE) methodology. This approach tested different cavity depths, diameters, chamfers, and opening sizes as well as the effect of a fine mesh covering. The resulting wind-tunnel test data was analyzed using a generalized additive statistical model (GAM). This approach quantified the relative effect of these parameters on the response variables of interest while accounting for non-linear frequency dependence. This experimental investigation showed that a mesh reduces the boundary layer noise by 8 dB. It was also shown that reducing the cavity area from the wall to the base of the microphone reduces the measured boundary layer spectral energy. Additionally, the model quantified the complex interactions between the mesh and area as well as the change in area.

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Section: Introductionmentioning

confidence: 99%

Design and Evaluation of Microphone Cavity Geometries for Wind-Tunnel Acoustic Measurements

VanDercreek

Majunath

Ragni

et al. 2019

AIAA Scitech 2019 Forum

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“…Relative to out-of-flow arrays, such sensors are subject to hydrodynamic noise from an energetic boundary layer over the sensing surface. As a consequence, a variety of passive and processing methods have been applied to mitigate this noise source and improve dynamic range, including recessing the array plate behind a porous wind screen 4,5,6,7 and cross-spectral matrix background noise subtraction 8,9 . For arrays placed either in or out of the flow, turbulence in the shear-or boundary-layer between the source and array, scatters sound from the target source, leading to measurement errors that grow with frequency, shear layer thickness, and turbulence level 10,11 .…”

Section: Introductionmentioning

confidence: 99%

Initial Calibrations and Wind Tunnel Test Results for an In-Flow Reference Array Using New In-Flow Acoustic Sources in Four Array Mount Configurations

Horne

Burnside

2018

2018 AIAA/CEAS Aeroacoustics Conference

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This paper describes efforts to develop a small in-flow phased microphone array as a reference acoustic sensor and quantify its level-measurement accuracy with new in-flow calibration sources. The devices can be applied to a wide variety of in-and out-of-flow measurement applications and test facilities. Recent tests of the array and two calibration sources in the NASA Anechoic Chamber and Army 7-by 10-ft Wind Tunnel at NASA Ames Research Center demonstrated that the array was functional over a frequency range of 2 to 100 kHz for emission angles of 92˚, 108˚, and 120˚, and Mach numbers of 0, 0.15, and 0.25. The array and calibration sources were then used to assess the relative effects of array installation on background noise and level measurement accuracy by locating the array in the flow (strut-and wall-mounted) as well as outside the flow behind a porous wall screen and a free shear layer. The wind tunnel array measurements were compared with anechoic chamber measurements using discrete microphones at the same source distance and emission angles. At 92˚, the noise floor and attenuation spectra were comparable (within 5 dB) for each installation from 2 to 30 kHz. At higher angles, the array installation behind the Kevlar screen had the lowest noise floor at M = 0.15 and 0.25. The array installation 10" (maximum available distance) behind a free shear layer had higher background noise that is typically reduced to a lower level by moving the array back further from the flow. For emission angles greater than 92˚, both the Kevlar and free shear layer installations exhibited stronger attenuations in measured level, beginning at lower frequencies than either the wallor strut mount configurations. Additional array and calibration source units of the same design are being tested at NASA's Glenn Research Center and Langley Research Center in their aeroacoustic research facilities in an effort to improve measurement accuracy and repeatability.

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“…The airtightness is ensured with silicone between the plywood and the bushing and with orings between the bushing and the microphones. The microphones are recessed in cylindrical apertures as proposed in [20] and openings in the wind-tunnel side walls are covered by a film of Kapton to protect from the hydrodynamic fluctuations. Kapton is a very thin film (0.0025 cm) similar to Kevlar.…”

Section: Laboratory Experiments: Set-upmentioning

confidence: 99%

Inverse problem with beamforming regularization matrix applied to sound source localization in closed wind-tunnel using microphone array

Padois

Gauthier

Berry

2014

Journal of Sound and Vibration

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Optimization of Microphone Array Wall Mountings in Closed-Section Wind Tunnels

Cited by 33 publications

References 10 publications

Design and Evaluation of Microphone Cavity Geometries for Wind-Tunnel Acoustic Measurements

Design and Evaluation of Microphone Cavity Geometries for Wind-Tunnel Acoustic Measurements

Initial Calibrations and Wind Tunnel Test Results for an In-Flow Reference Array Using New In-Flow Acoustic Sources in Four Array Mount Configurations

Inverse problem with beamforming regularization matrix applied to sound source localization in closed wind-tunnel using microphone array

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