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A directional array approach for the measurement of rotor noise source distributions with controlled spatial resolutionA special array system has been designed to examine noise source distributions over a helicopter rotor model. The particular measurement environment is for a rotor operating in the open jet of an anechoic wind tunnel. An out-of-flow directional microphone element array is used with a directivity pattern whose major directional lobe projects on the rotor disk. If significant contributions from extraneous tunnel noise sources in the direction of the side lobes are excluded, the dominant output from the array would be that noise emitted from the projected area on the rotor disk. The design incorporates an array element signal blending features which serves to control the spatial resolution of the size of the directional lobes. (Without blending, the resolution and side lobe size are very strong functions of frequency, which severely limits the array's usefulness).
Document ID
19870042585
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Brooks, T. F.
(NASA Langley Research Center Hampton, VA, United States)
Marcolini, M. A.
(NASA Langley Research Center Hampton, VA, United States)
Pope, D. S.
(PRC Kentron, Inc. Hampton, VA, United States)
Date Acquired
August 13, 2013
Publication Date
January 8, 1987
Publication Information
Publication: Journal of Sound and Vibration
Volume: 112
ISSN: 0022-460X
Subject Category
Aerodynamics
Accession Number
87A29859
Distribution Limits
Public
Copyright
Other

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