Slitted leading edge profiles for the reduction of turbulence-aerofoil interaction noise.

Abstract

Aerofoils operating in a turbulent flow are an efficient source of noise radiation by scattering vorticity into sound at the leading edge (LE). Much work has now been undertaken demonstrating the effectiveness of serrations, or undulations, introduced onto the LE can substantially reduce broadband LE interaction noise. However, all of this work is focused on sinusoidal LE serration profiles. In this paper, an alternative profile is proposed that is capable of providing significantly greater noise reductions than the maximum noise reductions that can be achieved by single-wavelength serrations of the same peak-to-root amplitude. In its most general realization, the LE serration profiles simply comprise of a sawtooth or single wavelength serration for which every root has a single narrow slit. This simple geometry, upon interaction with a turbulent flow, produces compact source regions at either end of the slit, which then destructively interfere, leading to considerably less efficient noise radiation than conventional single-wavelength geometries. The paper will demonstrate experimentally that even slits by themselves can provide greater levels of noise reduction than conventional profiles of the same peak-to-root amplitude.