Noise produced by a sawtooth trailing edge

An analysis is made of the noise produced by low Mach number turbulent flow over the serrated edge of a flat plate airfoil at zero angle of attack. The serrations are of sawtooth profile of wavelength λ and root-to-tip distance 2h. At frequencies ω satisfying ωh/U≫1 (where U is the velocity of the main stream) it is predicted that the intensity of the radiation is reduced relative to that produced by the same flow over an unserrated edge by at least 10×log[1+(4h/λ)2] dB. Predictions are contrasted with analogous results derived [M. S. Howe, J. Fluids Struct. 5, 33–45 (1991)] for smoothly varying serrations of sinusoidal profile, for which it was concluded that attenuations of order 10×log(6h/λ) dB are possible.