The Fraunhofer Institute for Wind Energy and Energy System Technology (IWES) located in Bremerhaven has taken the arduous job of opening a facility to test oversized rotor blades up to 90 meters length in the early part of summer this year.
For the purpose of bending the rotor blades of such magnitude, the new facility will incorporate a tiltable concrete mounting block made of 1,000 metric tons of steel and reinforced concrete. The hydraulic cylinders installed in the facility will tilt the block and extra cylinders will be utilized to load the blade. The loading of the blade will facilitate the engineers from IWES to bend the blades of the rotor to the required angle with ease.
For the purpose of testing, the flange of the rotor blade will be firmly mounted over the tilt block and the tip of the blade will be projected upwards at a predetermined angle. Loading cables meant for the purpose will be connected at different locations along side the blade and to the hydraulic cylinders kept over the floor. During the tilting process, the tilt block is rotated to enable upward movement of the blade. Its upward movement is neutralized by the downward pulling of the loading cables. The testing will allow the blades of 90 meter length to bend to a distance up to 25 meters. In 2009, IWES opened up a facility for testing rotor blades upto 70 meters length in Bremerhaven, but it lacked the tiltable mounting block.
The new facility in addition to extreme load testing is also equipped to replicate the cyclic forces enforced on the rotor blades due to wind force, which have a bearing over the rotor blades made of carbon or glass fiber. The facility utilizes a hydraulic cylinder to activate fatigue loading by making alternative push or pull on the blade in order to generate vertical or horizontal booming vibrations on the blades. The facility will subject the blades to the same amount of loads that a wind blade will endure in its 20 years of operation.
According to Falko Bürkner, the leader of the IWES blade testing team, the testing of the blades subjecting them to extreme conditions utilizing theoretical loading facility will ensure the blades to endure 100% design load, thus nullifying the anxiety of the manufacturers.
Source: http://www.fraunhofer.de/