Risø DTU's Wind Energy Division has been working on developing an innovative way to increase the efficiency of wind turbines by adding flexible rubber trailing edge flaps on the blades. The research institute has recently announced success in a wind tunnel test using the concept, which we initially covered back in March 2009. Basically, the new technology allows for better control of the load on the blades. The flexible trailing rubber edge flap is made of elastic material which is controllable through the use of compressed air or hydraulics. The new technology dubbed Controllable Rubber Trailing Edge Flap (CRTEF), has shown promising results in the wind tunnel test.

Currently used wind turbine blades can be up to 60 meters in length, and can flex as much as 4-6 meters when hit by strong gusts. This puts the blades under enormous stress, which contributes to shorter blade life and shorter service intervals. Since the blades can be quite long, there is a difference between the stress exerted on the blade in the lower part, near the hub, and the outer part, near the blade's tip. This is why Risø is currently exploring different types of sensors and plastic, rather than rubber, flaps along the blade's edge.

Here's an illustration of what the rubber flaps concept looks like:

The relatively slow pitch regulation of the blade, to adjust it according to wind conditions, can be compensated with the use of rubber flaps.

Take a look at this video which explains the wind tunnel testing activities and the concept.

The institute will be working on a full-scale prototype that can be deployed on an actual industry size wind turbine blade.

[source: Risø DTU]