DESIGN OF REDUCED NOISE AIRFOILS FOR WIND TURBINES

The topic of this paper is the reduction of trailing-edge noise which is considered to be the main noise mechanism on large, modern wind turbines. The noise reduction can either be achieved by applying serrated trailing-edges or by modifying the airfoil shape in a proper way. A prediction model for trailing-edge noise is used to study the influence of boundary- layer structure on the noise. It appears that a thin attached boundary layer is favorable for reducing trailing-edge noise. Based on this principle a number of airfoils were designed and tested with regard to the lift/drag characteristics, the boundary-layer structure, and the noise level they produce. It can be concluded that a reduction of 2-4 dB(A) is achievable by changing the airfoil shape. Furthermore, it could be confirmed that serrated trailing edges lead to a remarkable reduction of up to 6 dB(A) if they are applied in a proper way.