Collaborative efforts between Embry-Riddle Aeronautical University (ERAU) and the National Renewable Energy Laboratory (NREL) have resulted in an innovative dual-axis Phase-Locked EXcitation (PhLEX) resonant test method for structural fatigue testing of wind turbine blades. Laboratory fatigue test results give blade manufacturers important information regarding the structural integrity of their designs and can offer insight on how to further increase the strength and efficiency of these blades. The PhLEX test method applies loads in a manner that is more representative of wind loading experienced through field operation conditions as compared to current dual-axis quantum resonant methods. The method developed involves exciting the blade at resonance in the edge direction, while simultaneously applying a direct actuation force in the flap direction at the first edge frequency. As a proof of concept, this method was employed on a 9-meter (m) blade test article at NREL’s National Wind Technology Center (NWTC) located near Boulder, Colorado. Preliminary results show that the PhLEX method is able to control the phase angle between application of flap and edge loads while decreasing testing time due to faster test frequencies and the ability to maintain constant amplitude loading.

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