Remote detection of internal and subsurface damage in wind turbine blades using acoustic beamforming and infrared thermography

This work experimentally investigated the feasibility and complementarity of aeroacoustic and infrared thermography (IRT) techniques for detecting damage in rotating wind turbine blades under controlled wind tunnel conditions. Two representative types of damage were considered: trailing edge cracks and internal shear web delamination, created in the scaled blades manufactured in-house. Experiments were conducted in the open jet facility at Delft University of Technology. Acoustic measurements using a two-dimensional microphone array revealed that trailing edge cracks induce distinct tonal noise modifications, which depend on the effective trailing edge thickness and are captured through spectral analysis and acoustic beamforming. The crack-induced tonal noise peaks at a trailing-edge-thickness-based Strouhal number, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mi>S</mml:mi> <mml:msub> <mml:mrow> <mml:mi>t</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>h</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> , between 0.15 and 0.25. IRT, by contrast, are highly sensitive to internal structural features; delaminated regions exhibited localized temperature variations due to changes in thermal properties. Principal component thermography was applied to further enhance the visualization of the internal shear webs and internal delamination. The results demonstrate that the use of aeroacoustic and IRT methods provides a complementary strategy for detecting both edge and internal damage in wind turbine blades.