Flaps reduce wind turbine blade loads

The idea is to reduce dynamic blade loads. However, unlike those on aircraft, the flaps being developed by the Technical University of Denmark in Risø are elastomeric, and are made as integral parts of the blades. "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, "explained researcher Helge Aagaard Madsen. A patent was applied for in 2004, but it is only recently that funding from the Danish Ministry of Science, Technology and Innovation and the local Zealand regional government has enabled development to prototype stage. The trailing edge is either controlled in response to measurements of inflow to a Pitot tube attached to the front edge of the blade section or a from the load on a small profile section mounted in front of the main blade. The trailing edge itself is made of rubber with fibre reinforced cavities. The cavities and directional fibre reinforcement provide the desired movement when the cavities are 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" Madsen said. The prototype suits a blade airfoil section with a 1m chord and a section is now being produced and is to be tested inside a wind tunnel. Madsen added that, "If the results confirm our estimated performance, we will test the rubber trailing edge on a full-scale wind turbine within a few years." More information from hama@risoe.dtu.dk