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Initial Calibrations and Wind Tunnel Test Results for an In-Flow Reference Array Using New In-Flow Acoustic Sources in Four Array Mount ConfigurationsThis 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-foot Wind Tunnel at NASA Ames Research Center demonstrated that the array was functional over a frequency range of 2 to 100 kilohertz for emission angles of 92 degrees, 108 degrees, and 120 degrees, 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 degrees, the noise floor and attenuation spectra were comparable (within 5 decibels) for each installation from 2 to 30 kilohertz. 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 inches (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 degrees, both the Kevlar and free shear layer installations exhibited stronger attenuations in measured level, beginning at lower frequencies than either the wall- or 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.
Document ID
20190026584
Acquisition Source
Ames Research Center
Document Type
Conference Paper
Authors
Horne, Clifton
(NASA Ames Research Center Moffett Field, CA, United States)
Burnside, Nathan
(NASA Ames Research Center Moffett Field, CA, United States)
Date Acquired
June 24, 2019
Publication Date
June 25, 2018
Subject Category
Research And Support Facilities (Air)
Acoustics
Report/Patent Number
ARC-E-DAA-TN55290
AIAA-2018-2969
Meeting Information
Meeting: AIAA/CEAS Aeroacoustics Conference 2018
Location: Atlanta, GA
Country: United States
Start Date: June 25, 2018
End Date: June 29, 2018
Sponsors: American Institute of Aeronautics and Astronautics (AIAA), Council of European Aerospace Societies (CEAS)
Funding Number(s)
WBS: 081876.02.01.03
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
Technical Review
NASA Peer Committee
Keywords
Aeroacoustic Wind Tunnel Research
Phased Microphone Arrays
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