Continuous-wave line laser thermography for monitoring of rotating wind turbine blades

This article presents a continuous-wave line laser thermography system for monitoring of rotating wind turbine blades. The proposed continuous-wave line laser thermography system non-destructively inspects rotating blades by generating thermal waves on the target blades using a continuous-wave line laser beam and simultaneously recording the corresponding thermal wave propagation using an infrared camera. The continuous-wave line laser thermography system is positioned at a fixed point, and the blades are automatically scanned using the continuous-wave line laser thermography system as the blades rotate under normal operational conditions. A coordinate transform algorithm named "time-space-integrated coordination transform" is developed for precise damage evaluation in rotating blades. Time-space-integrated coordination transform transforms spatially and temporally varying thermal images taken by the infrared camera to only temporally varying thermal images viewed from the perspective of the fixed blade positions. The effectiveness of the proposed continuous-wave line laser thermography system is experimentally validated by detecting hidden delamination on lab-scale rotating blades. In the experiments, artificial delaminations with diameters of 15 and 30 mm are successfully visualized with no false alarms while the blades are rotating at 10 r/min.