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Rotor blade-vortex interaction noise reduction and vibration using higher harmonic controlThe use of higher harmonic control (HHC) of blade pitch to reduce blade-vortex interaction (BVI) noise is examined by means of a rotor acoustic test. A dynamically scaled, four-bladed, articulated rotor model was tested in a heavy gas (Freon-12) medium. Acoustic and vibration measurements were made for a large range of matched flight conditions where prescribed (open loop) HHC pitch schedules were superimposed on the normal (baseline) collective and cyclic trim pitch. A novel sound power measurement technique was developed to take advantage of the reverberance in the hard walled tunnel. Quantitative sound power results are presented for a 4/rev (4P) collective pitch HHC. By comparing the results using 4P HHC to corresponding baseline (no HHC) conditions, significant midfrequency noise reductions of 5-6 dB are found for low-speed descent conditions where BVI is most intense. For other flight conditions, noise is found to increase with the use of HHC. LF loading noise, as well as fixed and rotating frame vibration levels, show increased levels.
Document ID
19920053154
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Authors
Brooks, Thomas F.
(NASA Langley Research Center Hampton, VA, United States)
Booth, Earl R., Jr.
(NASA Langley Research Center Hampton, VA, United States)
Date Acquired
August 15, 2013
Publication Date
September 1, 1990
Subject Category
Acoustics
Accession Number
92A35778
Distribution Limits
Public
Copyright
Other

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