Noise reduction method

Abstract From the Canadian patent

When there is relative movement at a speed above a critical, value, between the trailing edge of a body such as a hydrofoil or, aerofoil section and a fluid, the fluid flow tends to form a pattern of discrete swirling vortices. Vortex shedding at each side of the trailing edge alternately can cause resonance or "singing" of the section. The effect of this phenomenon is reduced by forming contiguous triangular flat-faced notches in the major surfaces of the section, adjacent the trailing edge, but leaving the profile of the leading edge substantially undisturbed. The notches in one major surface are preferably staggered relative to those in the other major surface.