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Effect of rotor stiffness and lift offset on the aeroacoustics of a coaxial rotor in level flight

Kim, Hyo Wan and Duraisamy, Karthikeyan and Brown, Richard (2009) Effect of rotor stiffness and lift offset on the aeroacoustics of a coaxial rotor in level flight. In: 65th American Helicopter Society Annual Forum, 2009-05-27 - 2009-05-29, Texas, USA.

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    Abstract

    The acoustic characteristics of a twin contra-rotating coaxial rotor configuration with significant flapwise stiffness are investigated in steady forward flight. The Vorticity Transport Model is used to simulate the aerodynamics of the rotor system and the acoustic field is determined using the Ffowcs Williams-Hawkings equation implemented using the Farassat-1A formulation. Increasing the hub stiffness alters the strengths of the blade vortex interactions, particularly those between the upper and lower rotors, and affects the intensity and directivity of the blade vortex interaction noise produced by the system. The inter-rotor blade vortex interaction on the advancing side of the lower rotor is the principal source of the most intensively focused noise that is generated by a conventionally articulated coaxial rotor system. For stiffened coaxial rotors, this particular inter-rotor blade vortex interaction is weakened as a result of a broad redistribution in lateral loading, yielding a reduction in the intensity of the noise that is produced by this interaction. The spanwise distribution of loading on the rotors of a stiffened coaxial system can be modified further by altering the lateral partition of lift (or lift offset). It is shown that decreasing the lift offset has the effect of counteracting the redistribution of loading due to flapwise stiffness and hence increases the blade vortex interaction noise as well as the power consumed by the rotor. Conversely, a reduction in both the power consumption and the blade vortex interaction noise is observed if the lift offset is increased, with the maximum benefit of lift offset being achieved at high speed. The computational results suggest that the noise from the dominant inter-rotor blade vortex interaction can be ameliorated through the use of lift offset control on stiffened coaxial systems, to the extent that the noise produced by this interaction can be made to be comparable to that produced by the other, weaker interactions between the two rotors of the system.

    Item type: Conference or Workshop Item (Paper)
    ID code: 27493
    Keywords: aeroacoustics, coaxial rotor, vorticity transport model, Ffowcs Williams-Hawkings equation, Farassat-1A formulation, inter-rotor blade vortex interactions, Mechanical engineering and machinery, Motor vehicles. Aeronautics. Astronautics, Mechanical Engineering, Aerospace Engineering, Computational Mechanics, Modelling and Simulation
    Subjects: Technology > Mechanical engineering and machinery
    Technology > Motor vehicles. Aeronautics. Astronautics
    Department: Faculty of Engineering > Mechanical and Aerospace Engineering
    Related URLs:
    Depositing user: Ms Katrina May
    Date Deposited: 30 Sep 2010 14:52
    Last modified: 03 Jun 2014 17:24
    URI: http://strathprints.strath.ac.uk/id/eprint/27493

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