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Broadband rotor noise analysesThe various mechanisms which generate broadband noise on a range of rotors studied include load fluctuations due to inflow turbulence, due to turbulent boundary layers passing the blades' trailing edges, and due to tip vortex formation. Existing analyses are used and extensions to them are developed to make more accurate predictions of rotor noise spectra and to determine which mechanisms are important in which circumstances. Calculations based on the various prediction methods in existing experiments were compared. The present analyses are adequate to predict the spectra from a wide variety of experiments on fans, full scale and model scale helicopter rotors, wind turbines, and propellers to within about 5 to 10 dB. Better knowledge of the inflow turbulence improves the accuracy of the predictions. Results indicate that inflow turbulence noise depends strongly on ambient conditions and dominates at low frequencies. Trailing edge noise and tip vortex noise are important at higher frequencies if inflow turbulence is weak. Boundary layer trailing edge noise, important, for large sized rotors, increases slowly with angle of attack but not as rapidly as tip vortex noise.
Document ID
19840014297
Acquisition Source
Legacy CDMS
Document Type
Contractor Report (CR)
Authors
George, A. R. (Cornell Univ. Ithaca, NY, United States)
Chou, S. T. (Cornell Univ. Ithaca, NY, United States)
Date Acquired
September 4, 2013
Publication Date
April 1, 1984
Publication Information
Publisher: NASA
Subject Category
Acoustics
Report/Patent Number
NASA-CR-3797
NAS 1.26:3797
Accession Number
84N22365
Funding Number(s)
CONTRACT_GRANT: NAG1-107
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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