On the effects of anisotropic turbulence on leading edge noise

Abstract

This paper presents an investigation on the broadband noise produced by the interaction of anisotropic turbulence with isolated aerofoils. Computational aeroacoustic simulations are performed using a synthetic turbulence method with a linearised Euler solver. A comprehensive and fundamental parameter study on leading edge noise is presented to assess the effects of aerofoil thickness, mean flow Mach number, and angle of attack in the presence of moderately anisotropic turbulence. To this end, the streamwise-to-transverse length scale ratio is varied from 0.33 to 3, which can be representative of the anisotropy in the fan wakes from aero-engines, grid-generated turbulence in open-jet wind tunnel experiments, and rotors ingesting turbulent boundary layers. Anisotropic turbulence presents a significant redistribution of the energy in the turbulence spectra in comparison with an isotropic baseline, which affects the resulting noise spectra. It has been found that the noise spectra are mainly influenced by the transverse velocity component for the examined anisotropic flows. The frequency at which the noise spectrum is at a maximum only relies on the mean flow speed and the axial length scale of the anisotropic turbulent flow. Noise reduction due to aerofoil thickness at high frequencies follows a linear trend, but the amount of noise reduction is sensitive to the anisotropy in the flow. It is shown that the contribution of the streamwise disturbances and length scale become increasingly important for thick aerofoils at high Mach numbers and for aerofoils at non-zero angle of attack.