This study was conducted to investigate the impulsive acoustic characteristics of a lift-offset coaxial rotor in high-speed forward flight, as well as the impact of wake-grid resolution and turbulence modeling on acoustic prediction. High-fidelity computational fluid dynamics/computational structural dynamics loose-coupling simulations were performed for air-load prediction using the high-fidelity rotorcraft aeromechanics simulation software Helios, and impulsive loading noise was simulated using the acoustic prediction software PSU-WOPWOP at eight microphones positioned below the lower rotor plane. No significant discrepancy in air-load and acoustic predictions was found between the three turbulence modeling cases [Spalart–Allmaras (SA)–Reynolds-averaged Navier–Stokes, SA–detached-eddy simulation, and SA–delayed-detached-eddy simulation] with Δ finest = 10 % C tip . It was found that the Δ finest = 10 % C tip case showed a good convergence of impulsive loading noise at most microphones in terms of the wake-grid resolution. Isolated rotor simulations were also carried out to quantify the relative importance of the two impulsive loading-noise sources of a lift-offset coaxial rotor: self-blade–vortex interaction (BVI) and blade-crossover events. Contours of induced inflow ratio on the rotor disks revealed higher induced velocity for the lift-offset coaxial rotor than the isolated rotors. The higher induced flow ratio reduced the distribution of sectional normal force, strength of self-BVIs, and BVI noise of the lift-offset coaxial rotor. Even with the reduced BVI noise, the lift-offset coaxial rotor showed a dramatically higher impulsive sound-pressure level than the isolated rotors, especially at high speed, as a consequence of mainly blade-crossover events.


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    Title :

    Impulsive Loading Noise of a Lift-Offset Coaxial Rotor in High-Speed Forward Flight


    Contributors:

    Published in:

    AIAA Journal ; 58 , 2 ; 687-701


    Publication date :

    2020-02-01




    Type of media :

    Conference paper , Article (Journal)


    Type of material :

    Electronic Resource


    Language :

    English





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