Investigating effects of pure shear deformation in wind turbine blade sub-structures

This anchor is a Bladena’s license and it was developed to reduce the displacement between the two profiles of the leading edge throughout its use. A wind turbine blade is exposed to cyclic forces, bending moments and torsional moments. A combination of such load components may result in fatigue cracks, because of the structural deformation of the box girder. A typical damage found in blades in operation is longitudinal cracks near the leading edge. These cracks usually appear on the leading-edge in the max-chord area and they are believed to be caused by the cyclic stresses the blade undertakes during operation. The source of this phenomenon is believed to be due to shear deformation of the entire blade. To mitigate this problem the company Bladena has suggested to use diagonal reinforcement elements named “X-Stiffeners”. In the literature covering wind turbine blade design and analysis, no investigation relating to this failure mechanism has been found. In other industries, such as aeronautics (airplane wings, rotor blades for helicopters, etc.) and bridges, horizontal shear distortion is a well-known mechanism which is taken into account in the design process. Furthermore, the shear deformation changes direction, when the gravity load direction changes depending on the blade azimuth angle. The “torsional” load component has generally received less attention in the field of blade design. With my thesis I ask myself the goal to create a test set-up in order to investigate the shear stiffness of wind turbine sub-structure, with that will be probed the structural benefits that are obtained on a wind turbine commercial girder box using an anchor system X/CROSS-STIFFENER. The blade I studied is a 34 m blade manufactured be SSP-Technology A/S, the entire turbine has a rated power of 2.0 MW.

La mia tesi si inserisce all’interno di un progetto internazionale formato da un consorzio di aziende (EUDP), operanti nel settore delle turbine eoliche. In particolare l’elaborato rappresenta un progetto pilota per la realizzazione di un prototipo di rinforzo interno alla struttura della pala eolica (X/CROSS-STIFFENER). In questo settore il trend tecnologico è di aumentare progressivamente le dimensioni delle pale in modo da ottenere potenze prodotte sempre maggiori con costi specifici dell’energia elettrica prodotta minori. Tale trend richiede lo sviluppo di materiali e soluzioni che garantiscono elevate prestazioni in termini di rigidezza e resistenza tenendo conto di vincoli di peso e quindi costo. Di fatto all’aumentare delle dimensioni del rotore le forze in gioco diventano progressivamente più grandi e ciò richiede una continua ricerca in questo ambito.