If you’ve ever seen a commercial-scale wind turbine in real life, then you’ll know that they’re huge – a single blade can be as long as 60 meters (197 feet). Researchers from Denmark’s Risoe DTU National Laboratory for Sustainable Energy tell us that such blades can flex by up to six meters (20 feet) when subjected to strong wind gusts. Worse yet, that load is often not evenly distributed along the length of the blade, so it doesn’t flex evenly. Fortunately, the researchers are working on addressing this problem, by attaching flexible flaps to the trailing edges of the blades. These flaps come in the form of silicone rubber strips, which run the length of the entire blade. The result, we’re told, will be quieter, higher-output turbines.
The project has been in development since 2006. Last December, a two-meter (six-foot) blade section with one of the rubber edge flaps was tested in a wind tunnel. The results showed that the flap did indeed reduce the deforming forces on the blade, and that the rubber holds its shape even when exposed to heavy winds. A blade that isn’t flexing back and forth, needless to say, will generate power more efficiently. The researchers have also noted that the flaps could make the blade-construction process easier. Blades are currently assembled from two pieces, and the trailing edge must be ground down after they’re put together, to lessen wind noise. Using the flaps, a ready-made, even sharper edge could simply be applied in the form of one long rubber strip.
There is the still the matter, however, of the uneven distribution of wind shear across the surface of the blade. The wind tunnel tests showed that different curvatures of the flaps could compensate for different intensities and directions of wind, but how do you continuously adjust those curvatures? The Risoe team put two sensors on the front of their blade section, which measured wind speed and direction. The data from those sensors was fed into a pneumatic system inside the blade, which changed the shape of the flap by pumping air in or out of it. Presumably on an entire blade, there would be sensors all the way down the forward edge, and the trailing edge strip would be divided into cells that could each assume different curvatures as dictated.
Risoe DTU is now looking towards production and testing of a full-scale prototype. Its trailing edge flap is reminiscent of a forward edge design for turbine blades, previously covered in Gizmag.
