Thursday, 12 March 2009

Controllable rubber trailing edge flap to reduce loads on wind turbine blades

"Congratulation To Team RISO"

The trailing edge of wind turbine blades can be manufactured in an elastic material that makes it possible to control the shape of the trailing edge. This will reduce the considerably 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 aircrafts, where flaps regulate the lift during the most critical times such as at take-off and landing, "explains Helge Aagaard Madsen, Research Specialist on the project.

However, there is a difference. Whereas on aircrafts, movable flaps are non-deformable elements hinged to the trailing edge of the main wing, this new technique means a continuous surface of the profile on the wind turbine blade even when the trailing edge moves. The reason for this is that the trailing edge is constructed in elastic material and constitutes an integrated part of the main blade.

Robust design of rubber
In 2004 Risø DTU applied for the first patent for this basic technique of designing a flexible, movable trailing edge for a wind turbine blade. Since then there has been a significant development with regard to the project. By means of so-called "Gap-funding" provided by the Ministry of Science, Technology and Innovation and by the local Region Zealand it has been possible to develop such ideas into a prototype stage.

Profile section with a controllable, flexible trailing edge, which is controlled from measurements of inflow to the blade using a Pitot tube attached to the front edge of the blade section (above) or a trailing edge operated from the load on a small profile section mounted in front of the main blade (below)

Part of the research has been aimed at the design and development of a robust controllable trailing edge. This has now 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 Helge Aagaard.

Watch video of the flexible rubber trailing edge

Inside a wind tunnel
The size of the protype fits a blade airfoil section with a chord of one metre and such a blade section is now being produced and is going to be tested inside a wind tunnel.

The capability of the trailing edge to control the load on the 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 Helge Aagaard.

Source : RISO

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