3D calculations of aerofoil-turbulence interaction noise and the effect of wavy leading edges

In this paper, wavy leading edge serrations for reduction of the aerofoil-turbulence interaction (ATI) noise are investigated numerically. A flat-plate aerofoil is considered and an advanced method is suggested to synthetically generate flow turbulence via an in-flow boundary condition that is particularly suitable for three-dimensional aeroacoustic simulations. The synthetic inflow turbulence generator which is based on superposition of eddies is practically free of spurious noise and can be optimised to generate any required velocity spectra such as the von Karman spectrum. A correlation length scale is defined for the fluctuating pressure on the leading edge of the aerofoil, and it is found that the leading edge serrations effectively reduce this correlation length scale. In addition, it is postulated that increasing the noise reduction by increasing the serration amplitude will reach a maximum beyond which, no further enhancement in noise reduction characteristics of the serration can be achieved by increasing the serration amplitude. The noise reduction mechanism is further related to the deformation of vortical structures near the leading edge of serrations which is explained in detail and is consistent with calculated phase and coherence spectra along the leading edges.

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