Effect of Leading-Edge Serrations on Helicopter Blade–Vortex Interaction Noise

Authors:
  • JFJoel A. Feinerman
    Joel A. Feinerman
  • SKSudarshan Koushik
    Sudarshan Koushik
  • FSFredric H. Schmitz
    Fredric H. Schmitz
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Abstract
The acoustic benefits of a serrated leading edge rotor blade are experimentally explored and compared with a more conventional rotor blade with a straight leading edge. An experimental simulation called the blade-controlled disturbance interaction (BCDI), in which a hovering rotor blade rotates through a stationary gust field, is employed. It has been shown previously that this controlled gust disturbance simulates a part of the induced velocity field resulting from blade–vortex interaction. Up to 3 dB of peak-to-peak noise reductions in the primary radiation direction were shown for the serrated blade encountering a parallel interaction. Lesser noise reductions were measured in off-axis directions. For more oblique interactions, noise reductions were observed to be spread over a much wider region of space. A simple theory is presented that explains the measured trends and the basic phase cancellation mechanism believed to be predominantly responsible for the reduced BCDI noise levels.