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High-speed helicopter rotor noise - Shock waves as a potent source of soundIn this paper we discuss the problem of high speed rotor noise prediction. In particular, we propose that from the point of view of the acoustic analogy, shocks around rotating blades are sources of sound. We show that, although for a wing at uniform steady rectilinear motion with shocks the volume quadrupole and shock sources cancel in the far field to the order of 1/r, this cannot happen for rotating blades. In this case, some cancellation between volume quadrupoles and shock sources occurs, yet the remaining shock noise contribution is still potent. A formula for shock noise prediction is presented based on mapping the deformable shock surface to a time independent region. The resulting equation is similar to Formulation 1A of Langley. Shock noise prediction for a hovering model rotor for which experimental noise data exist is presented. The comparison of measured and predicted acoustic data shows good agreement.
Document ID
19930045406
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Authors
Farassat, F.
(NASA Langley Research Center Hampton, VA, United States)
Lee, Yung-Jang
(NASA Langley Research Center Hampton, VA, United States)
Tadghighi, H.
(NASA Langley Research Center Hampton, VA, United States)
Holz, R.
(McDonnell Douglas Helicopter Co. Mesa, AZ, United States)
Date Acquired
August 16, 2013
Publication Date
January 1, 1991
Publication Information
Publication: In: AHS and Royal Aeronautical Society, Technical Specialists' Meeting on Rotorcraft Acoustics(Fluid Dynamics, Philadelphia, PA, Oct. 15-17, 1991, Proceedings (A93-29401 10-71)
Publisher: American Helicopter Society
Subject Category
Acoustics
Accession Number
93A29403
Distribution Limits
Public
Copyright
Other

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