On the superior performance of leading edge slits over serrations for the reduction of aerofoil interaction noise

Chaitanya, Paruchuri, Joseph, Phillip and Ayton, Lorna J. (2018) On the superior performance of leading edge slits over serrations for the reduction of aerofoil interaction noise. In 2018 AIAA/CEAS Aeroacoustics Conference. American Institute of Aeronautics and Astronautics.. (doi:10.2514/6.2018-4107).

Abstract

Aerofoils operating in a turbulent flow are an efficient source of noise radiation by scattering vorticity into sound at the leading edge. Much work has now been undertaken demonstrating the effectiveness by which serrations, or undulations, introduced onto the leading edge, can substantially reduce broadband leading edge interaction noise. However, all of this work is focused on sinusoidal leading edge serration profiles. In this paper, a family of alternative serration profiles are proposed that are capable of providing significantly greater noise reductions than single-wavelength serrations at optimal conditions. This new family of profiles will be shown to reduce interaction noise through a fundamentally different noise reduction mechanism than conventional single-wavelength profiles. Unlike single-wavelength profiles, which produce a single compact dominant source region per serration wavelength, these new profiles are designed to produce two dominant compact sources per serration wavelength of the same source strength, that are separated in the streamwise direction. Since these sources are arranged to be closer together than the turbulence length-scale, they are highly coherent and therefore radiate with a difference in phase. A frequency therefore exists at which the sources are exactly 180° out of phase leading to very high levels of noise reduction in the far field.

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