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

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 (BVI). 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.