PSI - Issue 68

Hugo Mesquita Vasconcelos et al. / Procedia Structural Integrity 68 (2025) 795–801 Hugo Mesquita Vasconcelos et al. / Structural Integrity Procedia 00 (2025) 000–000

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3. Results and Discussion The acquisition took place in late January under clear skies with plenty of sunlight. The first set of thermal images was captured at 10:55, followed by a second set at 13:25. There was a light breeze with wind speeds below 3 m/s. Since thermographic imaging requires the turbine blade to be stationary, a malfunctioning wind turbine that was already stopped was chosen, thereby avoiding additional downtime costs. The turbine under study featured 29-meter blades with 1.5-meter extensions glued. The extensions have been in place since 2016, with the turbine operating since 2005. As anticipated, the initial thermal images confirmed that a comprehensive structural integrity assessment could not be achieved by capturing the entire blade in a single image due to the low resolution of the infrared camera. The full-length thermal image of the blade resulted in a resolution of 60 mm per pixel, which is insufficient for detecting small-scale defects, as shown in Fig. 3.

Fig. 3. Full blade low-resolution thermal acquisition (60mm/px)

Consequently, it became necessary to focus on smaller sections of the blade for each analysis rather than attempting to examine the entire blade at once. This approach allowed for a higher resolution of the thermal images and enabled a more detailed analysis of the blade's structural integrity. By segmenting the blade into smaller areas, the resolution improved significantly, enhancing the ability to detect and analyse potential defects that would have been missed in a full-length capture. Although the entire blade was analysed in smaller parts, the most detailed and significant observations were made in the last 4 meters of the blade. The thermal images obtained directly from the DJI acquisition system are presented in Fig.4. These images reveal several features: two distinct lines in the middle, a black hole on the bottom right, and three additional holes at the top. These holes, commonly present in wind turbine blades, are designed to allow water drainage from the blade's interior and are also visible in the visible light spectrum images. The holes can also be used as either lightning receptors or balancing weights, depending on the blade’s manufacturer. Besides it is also possible to visualize a 10 Celsius degree average difference between acquisitions. In this acquisition, a resolution of 7mm per pixel was achieved which is a much better resolution to perform a proper analysis.

Fig. 4. Thermal and visible light images acquisition from DJI system