Investigation of the Vortex Noise Produced by a Helicopter Rotor
Final technical rept.
ROCHESTER APPLIED SCIENCE ASSOCIATES NY
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Karman-street-type vortex shedding from a lifting surface was analyzed as a source of noise from a helicopter rotor in hover and forward flight. Experimental pressure-time histories were analyzed, and high resolution spectra were developed over a frequency range of 0 to 5000 Hz using a 0.7-Hz filter. The results of the investigation indicated that vortex noise is the major source of acoustic radiation from a helicopter rotor in hover or low-speed flight and that it is concentrated in the frequency range of 200 to 500 Hz.