Vibration characteristic of wind turbine blades in fatigue loading test

A set of single-exciter fatigue loading scheme driven by an unbalanced shaft was designed in order to perform the fatigue test for wind turbine blades. To analyze the vibration characteristic of blade, the modal tests were carried out firstly on aeroblade 2.0-45.3 wind turbine blade to acquire the low-order natural frequency 1st = 0.88 Hz and 2nd = 2.72 Hz in the minimum flapwise direction respectively. Then, the vibration mathematical model of fatigue loading equipment was deduced based on Lagrange equation, and the parameters affecting blade vibration rules were obtained. Next, the simulation model was built with Matlab/Simulink software, and vibration characteristics of the wind turbine blade under different loading frequencies were also obtained. When the loading frequency was 0.80 Hz, the amplitude of the loading point became disorder. When the loading frequency increased to 0.84 Hz continuously, the amplitude of the loading point was stable at around 400 mm. When the loading frequency was 0.88 Hz which was equal to the first-order natural frequency of the blade, the amplitude reached 1000 mm. At this time, resonance phenomenon occurred, which could cause fatigue damage to the blade greatly. When the loading frequency continued to increase to 0.92 Hz, the amplitude reduced to about 400 mm. Finally, a set of single-exciter fatigue loading system for the wind turbine blade was established, and test verification on the blade vibration characteristics was carried out. Test results were basically consistent with the simulation results, thus the validity of mathematical model and simulation model were verified. The above conclusions have important reference value for fatigue loading test of wind turbine blades.