Compared with other rotor blade prototypes measuring more than 80m, this test object is small, nevertheless it is certainly keeping Fraunhofer Institute for Wind Energy (IWES) scientists on their toes. For the very first time, a rotor blade with bend-twist coupling was tested. When subject to aerodynamic loads, the prebend of the blade results in mechanical deformation during operation, the purpose of which is to mitigate the loads on the overall structure. Following further tests, three identical models will be constructed by the German Aerospace Centre (DLR) and shipped to the USA. The blades will then be installed there on a research turbine for a measurement campaign lasting several months. These activities will all take place within the scope of the SmartBlades2 research project.
The static rotor blade test is always highly anticipated by blade manufacturers. The prototype’s structural design must be able to withstand the load of a simulated extreme gust. In addition to testing of the two flap and edgewise directions, testing of a rotor blade with bend-twist coupling (BTC) also comprises a torsion test. “Although the setup for the rotor blade torsion test is similar to the scenario for static testing, it is in fact more complex as the additional deformation has to be measured precisely,” said IWES test engineer Tobias Rissmann summarising the particular challenge of the test. During the subsequent dynamic tests, the stresses incurred over the entire service life of the rotor blade spanning 20 years are simulated in a drastically reduced time frame.