Numerical Prediction of Tonal Aeroacoustic Noise Produced by Small Wind Turbines

Abstract

Abstract The aeroacoustic design of small wind turbines (SWTs) can be challenging due to the possibility of the low Reynolds number (Re) flow over the blades generating tonal noise. The numerical prediction of this tonal noise using computational aeroacoustics can improve the understanding of the flow mechanisms behind the tonal noise to improve SWT blade design. In this study, wall-resolved incompressible large eddy simulation (LES) and the Ffowcs-Williams and Hawkings (FW-H) acoustic analogy are applied to a low Re airfoil, SD 7037, at Re = 4.1 × 104 to assess the ability of this method to predict tonal noise. The tonal prediction at 1° angle of attack aligned with experimental measurements and further analysis confirmed that the Kelvin-Helmholtz (K-H) rolls in the suction side laminar separation bubble (LSB) are the source of the aeroacoustic tone. The tone is due to the K-H rolls passing the trailing edge of the airfoil, and a secondary tone intermittently appears due to a 3D instability in the K-H roll. The accurate prediction of tonal noise using LES and FW-H opens the possibility of incorporating this method into the aeroacoustic design of low Re airfoils used for SWTs.