Development of design tools for reduced aerodynamic noise wind turbines

Informazioni relative al progetto

ID dell’accordo di sovvenzione: JOR3950083

Progetto chiuso

Data di avvio 1 Gennaio 1996

Data di completamento 31 Dicembre 1997

Finanziato da

• Specific programme for research and technological development, including demonstration in the field of non-nuclear energy, 1994-1998

Costo totale

Nessun dato

Contributo UE

Nessun dato

Coordinato da

UNIVERSITAET STUTTGART
Germany

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Risultati sfruttabili

Development of design tools for reduced aerodynamic noise wind turbines; DRAW

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 wind turbine can be expected or whether it will be masked by the noise coming from the rest of the blade. Measurements were carried out on two commercial wind turbines in the Netherlands. For this different techniques were applied, i.e. ground boards and an acoustic parabola which allows to discriminate between different parts of the blades. Another objective of the project was the development of a design tool for wind farms. The resulting computer code (dB DRAW) allows to predict the noise, which results from an arbitrary distribution of wind turbines, at several emission points. The handling of the code is based on a graphical user-interface which enables the user to locate turbines in a wind farm using simple mouse operations. The program is therefore extremely user-friendly.