Slitted leading-edge proles for the reduction of broadband interaction noise

Abstract

Aerofoil Turbulence Interaction (ATI) noise is an inviscid phenomenon generated by the impingement of turbulent flows onto the leading-edge of an aerofoil. This thesis deals with a novel leading-edge serration geometry, composed of narrow slits, to reduce ATI noise. These profiles have been recently found to provide significantly better noise reductions than conventional leading edge geometries. A numerical and analytic investigation is performed into the mechanism and performance of its noise reduction. The far-field radiation is shown to be influenced by a system of induced vortices affecting the distribution of sources on the flat-plate and by destructive interference between the two sources generated at both ends of the slit. A simple two-source model is developed to predict the far-field noise reduction obtained and compared to straight leading-edge aerofoils. A numerical parametric study is also performed, aimed at providing greater insight and understanding into the sensitivity of noise reductions to variations in the slit geometrical parameters. In particular, this thesis investigates the effect on source strength distribution to variations in slit length, width and wavelength and elucidates the reason for this effect on source distribution in terms of the fundamental vortex dynamics. This thesis concludes with an extensive experimental study into the effect on control performance due to variation in slit geometry, aimed at validating the numerical findings and providing guidelines for optimising slitted leading-edge profiles.

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