Experimental and Numerical Full-Field Displacement and Strain Characterization of Wind Turbine Blade Using a 3D Scanning Laser Doppler Vibrometer

Full-field dynamic measurement is desirable and useful for many purposes including model validation, or experimental characterization of test articles for which a finite element model is not available. Surface full-field strain measurement and test-model correlation have been performed on a small-size isotropic structure with a non-contacting 3D Scanning Laser Doppler Vibrometer (SLDV), which has an advantage over strain gauge tests with measurements at only a few discrete points. However, the application on large-size anisotropic structures has not been explored. This is the first work using the 3D SLDV for measuring the full-field displacement and strain Operational Deflection Shapes (ODSs) of a large composite structure, a 4.2-meter wind turbine blade. The displacement and strain measurement results are also correlated to the corresponding predictions of the blade composite finite element model in both a visual and quantified manner. The correlation is demonstrated for both low-frequency fundamental modes, but also for complex, highly-coupled high-frequency modes, which is challenging for other optical methods. Correlation results show a high degree of agreement between measured and numerically predicted displacements and strains, demonstrating the validity of the 3D SLDV measurement and the developed finite element model of the composite blade. The strain shapes are also compared with the displacement shapes and the blade structural configuration to reveal the effect of the blade structure on the strain distribution. The full-field displacement and strain identified and the proposed measurement and correlation technique would benefit wind turbine blade designers by providing new experimental tools to evaluate blade structural performance and reliability and provides a useful reference for blade structural designers.