A numerical simulation of noise generation during closed‐loop vibration reduction using actively controlled flaps (ACFs) has been conducted. To develop this simulation capability, a rotor aerodynamic model generating unsteady time‐domain blade surface pressure distributions
and including effects of compressibility and a free‐wake was developed. This aerodynamic tool was incorporated into an aeroelastic model featuring fully coupled flap‐lag‐torsional dynamics and including moderate deflections. An acoustic prediction tool based on WOPWOP
was also introduced and modified to fully account for blade flexibility on noise generation. This unified aeroelastic/aeroacoustic analysis program was validated with experimental aerodynamic and acoustic data. Single and dual ACF configurations were used to reduce 4/rev vibrations in descending
flight, where heavy blade‐vortex interaction (BVI) effects are expected, and the accompanying changes to noise generation were carefully examined. It was observed that noise on a carpet plane beneath the rotor increases by 1–3 dB for all ACF vibration reduction configurations
simulated. However, imposing saturation limits on flap deflections and using the dual flap configuration was found to reduce the acoustic penalty as a result of vibration reduction.
Department of Aerospace Engineering, University of Michigan, Ann Arbor, Michigan
Publication date: January 1, 2005
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