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Stall induced vibrations in stall regulated wind turbines

The possiblity of stall induced vibrations as predicted by aeroelastic calculations has to some extent been hindering the developed of large stall regulated wind turbines. A continuous upscaling of smaller turbines has been going on, in general without serious vibrational problems showing up. However the behaviour in stall has not been based on a sufficient proper prediction method and the phenomena are not fully understood.

Measurements from 3 of the 4 turbines involved in this project have been analyzed and all 4 turbines have been modelled. Different stall models are implemented in the aeroelastic codes, and the responses of the turbines are quite well predicted, though with less success for the WPX-20 rotor. This is the only one that has a high vibrational level in stall. Some of the causes for this are predictable, but for some reason not yet understood, 3-dimensional aerodynamic effects are not present for this rotor.

Inclusion of the time delay stall model generally increases damping, but does not create absolute stability for a single blade section. However when integrated over the whole blade stability is obtained.

The dynamic stall models have been tested with aerofoil section measurements. Some of the hysteresis characteristics are quite well modelled, but overall agreement is not obtained, which accordingly is reflected in the total response calculation. The uncertain aspects with respect to prediction of stall induced vibrations on design level are ways to account for 3-dimensional effects and dynamic stall (in combination) for specific aerofoils and blade shapes.

Reported by

RISOE National Laboratory
4000 Roskilde
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