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The project has consisted in development and testing of a two-bladed soft rotor for an existing 15 kW flexible wind turbine. The new concept is characterised as a free yawing down wind turbine with nacelle tilting flexibility and a two-bladed teetering rotor with three-point supported blades with build-in structural couplings. The power and the loads are controlled by active stall and active coning.

The project has constituted a design process, however with the main emphasis on determination of optimal characteristics for the turbine, perceived as a universal concept.

The concept has been developed by extensive application of aeroelastic predictions, numerical optimisation and stability analysis in order to obtain optimal aeroelastic response and minimal loads. The calculations and succeeding model tests have been performed particularly for a 13 m diameter rotor, but all conceptual design principles have been focused on application to large MW turbines. The intention with this has been to make the results generally applicable and not limited to the development of the specific wind turbine.

The flexible blades and the principle of active coning allows the blades to deflect with the wind to such an extent that the loads are much reduced during stand still in extreme winds. Comparisons of predictions for this concept and a similar rigid rotor show that the blade and rotor loads are reduced to between 25 and 50 % during operation as well as during stand still in extreme winds. This, however, is not a universal ratio for the relation between the loads on the two concepts. In particular this relation depends upon the size of the turbine.

The aeroelastic predictions have covered normal operation, stand still in extreme winds and abnormal upwind operation. Corresponding conditions have been investigated with the prototype turbine, and the measurements have to a large extent verified the predicted turbine characteristics. The turbine has been operating perfe

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