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An efficient and robust method for predicting helicopter rotor high-speed impulsive noiseA new formulation for the Ffowcs Williams-Hawkings quadrupole source, which is valid for a far-field in-plane observer, is presented. The far-field approximation is new and unique in that no further approximation of the quadrupole source strength is made and integrands with r(exp -2) and r(exp -3) dependence are retained. This paper focuses on the development of a retarded-time formulation in which time derivatives are analytically taken inside the integrals to avoid unnecessary computational work when the observer moves with the rotor. The new quadrupole formulation is similar to Farassat's thickness and loading formulation 1A. Quadrupole noise prediction is carried out in two parts: a preprocessing stage in which the previously computed flow field is integrated in the direction normal to the rotor disk, and a noise computation stage in which quadrupole surface integrals are evaluated for a particular observer position. Preliminary predictions for hover and forward flight agree well with experimental data. The method is robust and requires computer resources comparable to thickness and loading noise prediction.
Document ID
19960016673
Acquisition Source
Langley Research Center
Document Type
Conference Paper
Authors
Brentner, Kenneth S.
(NASA Langley Research Center Hampton, VA United States)
Date Acquired
September 6, 2013
Publication Date
January 1, 1996
Subject Category
Acoustics
Report/Patent Number
NASA-TM-111251
NAS 1.15:111251
AIAA Paper 96-0151
Meeting Information
Meeting: 34th Aerospace Sciences Meeting and Exhibit
Location: Reno, NV
Country: United States
Start Date: January 15, 1996
End Date: January 18, 1996
Accession Number
96N22286
Distribution Limits
Public
Copyright
Public Use Permitted.
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