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Rubber flap reduces wind turbine blade loads

A controllable rubber trailing edge flap can reduce the loads on wind turbine blades, according to Risø Technical University Denmark (DTU).

If the trailing edge of wind turbine blades is manufactured with an elastic material, the shape of the trailing edge can be controlled, reducing the dynamic loads that large wind turbine blades are exposed to during operation.

“Providing the blade with a movable trailing edge it is possible to control the load on the blade and extend the life time of the wind turbine components. This is similar to the technique used on aircraft, where flaps regulate the lift during the most critical times such as at take-off and landing,” says Helge Aagaard Madsen, Research Specialist on the project at Risø DTU.

However, there is a difference. Whereas on aircraft, movable flaps are non-deformable elements hinged to the trailing edge of the main wing, the technique from Risø DTU results in a continuous surface of the profile on the wind turbine blade even when the trailing edge moves. This is achieved by constructing the trailing edge in elastic material and as an integrated part of the main wind turbine blade.

Part of the research has been aimed at the design and development of a robust controllable trailing edge. This has led to the manufacturing of a trailing edge of rubber with built-in cavities that are fibre reinforced. The cavities in combination with the directional fibre reinforcement provide the desired movement of the trailing edge, when the cavities are being put under pressure by air or water.

“In this project a number of different prototypes have been manufactured with a chord length of 15 cm and a length of 30 cm. The best version shows very promising results in terms of deflection and in terms of the speed of the deflection” says Madsen.

The capability of the trailing edge to control the load on the wind turbine blade section is going to be tested in a wind tunnel. This part of the development process is supported by GAP-funding from Region Zealand.

”If the results confirm our estimated performance, we will test the rubber trailing edge on a full-scale wind turbine within a few years” says Madsen.

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