Rotor Broadband Noise Resulting from Tip Vortex/Blade Interaction

The study described was conducted to investigate tip vortex/blade interaction as a source of broadband noise to hovering helicopter rotors. Observations of full scale, multi-blade rotors indicate that at moderate to high lift conditions the tip vortex, passing beneath a blade caused a stall pocket t...

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Bibliographic Details
Main Authors: Munch,Charles L, Patterson,Robert W, Day,Henry
Format: Report
Language:English
Subjects:
ACOUSTIC SIGNATURES
Acoustics
AERODYNAMIC DRAG
HELICOPTER ROTORS
Helicopters
NOISE
ROTOR BLADES(ROTARY WINGS)
VORTICES
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Summary:The study described was conducted to investigate tip vortex/blade interaction as a source of broadband noise to hovering helicopter rotors. Observations of full scale, multi-blade rotors indicate that at moderate to high lift conditions the tip vortex, passing beneath a blade caused a stall pocket to form near the blade tip. At these same lift conditions rotor noise (expressed as Perceived Noise Level) was observed to increase at a faster rate than for lower lift conditions. This behavior has been termed 'noise divergence.' An experimental investigation was conducted in the UARL Acoustic Research Wind Tunnel to define the noise characteristics associated with this tip vortex/blade interaction.