Full-field deformation measurement of wind turbine blades using digital image correlation

Traditional digital image correlation (DIC) method is always invalid for measuring deformation of object's surface when large rotational angle occurs. In order to solve this problem, an improved DIC method based on rotated subset is proposed to measure deformation of wind turbine blades. Firstly, an approximate rotational angle of deformed subset is calculated using feature points detecting technique. Then, the deformed subset is rotated and matched with the reference subset in integer pixel search stage. Finally, a modified NR iteration algorithm considering rotated subset is proposed for the subpixel registration. Simulated experiments prove the method is valid for measuring full-field deformation with random rotations. The average correlation coefficient reaches 0.99 that shows the proposed DIC method achieves high-quality correlation matching. Then three-dimensional deformation of a 5 kW wind turbine blades is measured based on proposed DIC method and dual-cameras system. The full-field displacement and time domain signals in three-dimensional direction are obtained. Results demonstrate that the proposed DIC method is suitable for measuring the deformation of rotating blades and shows great potential on the deformation measurement of large wind turbine blades in operation. © 2018, Science Press. All right reserved.