Effect of airfoil thickness on gust–airfoil interaction noise

Abstract

Interaction between turbulence and an airfoil is a significant aerodynamic noise source for many engineering applications when turbulence in the wake of upstream blades interacts with the leading edge of downstream blades. Modeling the oncoming turbulence as harmonic gusts is a common approach to study the noise generated by turbulence–airfoil interaction. In former studies, it has been found that the sound reduces with the increase in airfoil thickness. However, this is not always true for high-reduced frequency cases. This paper studies airfoil thickness effects using a computational aeroacoustics approach based on the spectral/hp element method. It is found that the sound pressure decreases with the increase in thickness for low-reduced frequency gusts. However, the sound pressure increases in the upstream direction and declines downstream with the increase in thickness for high-reduced frequency cases. To reveal its mechanism, a semi-analytical method and the convective Ffowcs Williams–Hawkings equation are used for low- and high-reduced frequency, respectively, to analyze the radiated noise. For low-reduced frequency cases, the sound reduction due to thickness is caused by the decrease in amplitude in the leading edge region and the increase in phase difference along the airfoil. For high-reduced frequency cases, the phase difference in the upstream observer is much more significant than the downstream observer's due to the convective effect. The increase in phase difference results in a cancellation effect, which leads to a different behavior upstream.