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The major aim of the present project was the development of new prediction models for the aerodynamic noise generation at wind turbine blades. These models should be transferred to computer codes and should be sensitive enough to consider even small changes in the airfoil geometry. This accuracy is needed in order to allow potential users in industry and research establishments to design silent airfoils and consequently blades and wind turbines.

The two main noise mechanisms - trailing-edge noise and inflow-turbulence noise - were treated separately with a mixture of experimental, theoretical, and numerical work. A prediction model for trailing-edge noise was developed which uses the spectrum of the pressure fluctuations beneath the turbulent boundary layer as an intermediate step. The model requires detailed information on the structure of the boundary layer close to the trailing edge. This information can result from Navier-Stokes simulations or from measurements. The model was validated on the result of acoustic measurements on airfoil sections and a good agreement was achieved. A fast and user-friendly Navier-Stokes code was developed which will serve as a future basis for the prediction of trailing-edge noise.

A new prediction model for inflow-turbulence noise is based on an acoustic analogy and makes use of the boundary-element method. The model is able to accurately predict the difference in noise production which is due to airfoil shape. A first design of a silent airfoil turned out to be successful. Both prediction models are believed to be useful also in related areas like fan or propeller noise.

Additional experiments on two different tip shapes revealed that a sword-like shape is more silent than a commonly used rounded tip. Furthermore, tip noise is limited to relatively high frequencies. However, the experimental techniques which were available did not allow to judge whether a distinct contribution of the tip to the total noise level of a win

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