Blade-Vortex Interaction Noise Characteristics of a Full-Scale Active Flap Rotor

Acoustic measurements of a full-scale active flap rotor obtained from the joint Boeing/DARPA /NASA/Army test in the Air Force National Full-Scale Aerodynamic Complex 40- by 80-foot anechoic wind tunnel demonstrated the potential of active flaps to reduce blade-vortex interaction (BVI) noise over a w...

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Bibliographic Details
Main Authors: JanakiRam, Ram D, Sim, Ben W, Kitaplioglu, Cahit, Straub, Friedrich K
Format: Report
Language:English
Subjects:
Acoustics
AERODYNAMIC NOISE
Aerodynamics
BLADE VORTEX INTERACTION
FLAP ROTORS
FLAPS(CONTROL SURFACES)
Helicopters
NOISE REDUCTION
RADIATED NOISE
ROTOR BLADES(ROTARY WINGS)
ROTORS
SYMPOSIA
VORTICES
WIND TUNNEL TESTS
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Summary:Acoustic measurements of a full-scale active flap rotor obtained from the joint Boeing/DARPA /NASA/Army test in the Air Force National Full-Scale Aerodynamic Complex 40- by 80-foot anechoic wind tunnel demonstrated the potential of active flaps to reduce blade-vortex interaction (BVI) noise over a wide range of directivity angles underneath the advancing rotor disk. The active flap rotor is a full-scale MD 900 helicopter main rotor with all of its five blades modified to include an on-blade piezoelectric actuator-driven flap with a span of 18% radius, 25% chord and located at 83% radius. Results are shown for three simulated descent flight conditions where BVI noise radiation was expected to be dominant for the baseline rotor. The baseline rotor for each test condition was simulated with 0 deg flap deflections (achieved via closed loop flap position control) on all the blades. For each test condition, open-loop single harmonic flap excitations with varying frequencies (2- to 5-per-rev), input phase and amplitude were used to demonstrate BVI noise reductions. Active flap schedules were identified which showed BVI noise reductions varying from 2 to 7 dB depending on the flight speed. Predictions made with CAMRAD II/PSU-WOPWOP code did not correlate well with active flap test data although the BVI noise levels for baseline rotor were well predicted for the low speed test cases. Hub loads increased for active flap schedules used for BVI noise reduction. Presented at the American Helicopter Society 65th Annual Forum, Grapevine, Texas, May 27-29, 2009.