Riso DTU's wind energy division has tested a controllable rubber trailing edge flap in a wind tunnel. The purpose of the test is to control loads on large wind turbine blades using a trailing edge made of an elastic material that can be controlled by means of compressed air or hydraulics.
Today's wind turbine blades, which can measure more than 60 meters in length, are subjected to enormous loads, which means that a blade can flex as much as four meters to 6 meters during strong gusts. However, the blades are also so long that there can be considerable differences in the loading from the gusts along the blade, according to Riso DTU. In wind farms, surrounding wind turbines also exert considerable influence and generate turbulence, which has a more localized effect.
The rubber trailing edge was tested in the open-jet wind tunnel at Velux in Denmark. The test setup consisted of a two-meter-long blade section with a total chord of one meter and a 15-cm rubber flap covering the entire span. The blade incorporated a pneumatic system for controlling the flexible silicone material, of which the trailing edge is made. Finally, two sensors were attached to the front of the blade that measured wind direction and speed.
‘The wind tunnel test showed, among other things, that the outward curve of the flap does not change markedly when subjected to wind loads similar to those on a real turbine blade,’ says Helge Aagaard Madsen, a research specialist at Riso DTU. ‘In addition, we measured the correlation between the deflection of the flap and the change in lift on the blade section. This produced figures which we can enter into our calculation models and then realistically simulate how the flap will reduce the loads on the turbine.’
The next step in the project is to develop the technology toward a stage where the rubber trailing edge flap is ready for testing in a full-scale prototype model, according to Riso DTU. The researchers will work on optimizing the design so the deflection will be as big as possible for a given pressure in the voids within the trailing edge.
SOURCE: Riso DTU