On the validation of aeroelastic simulations of wind turbines using digital image correlation

The modern development of wind turbines (WT) is driving a consistent growth in rotor size. With longer rotor blades, the need for accurate validation of aeroelastic simulations becomes more significant. This thesis provides a validation of aeroelastic simulations of WTs through a comparison with field measurements. The focus is on rotor blade deformation and torsion, as these values gain significance with the structural evolution of rotor blades. These can be measured by optical measurement techniques, such as Digital Image Correlation (DIC). Since DIC is highly dependent on weather conditions, the availability of measurements over a long period of time is limited. The question is, whether DIC can be used to validate aeroelastic simulations of WTs. A short introduction to all relevant fields of interest, such as basics of WTs, lidar measurements, aeroelastic models and their validation, as well as DIC and other relevant rotor blade deformation measurement techniques is given. Afterwards, a measurement setup is defined to evaluate the potential of DIC. A measurement campaign was carried out during January 2019 at the National Wind Technology Center (NWTC) of the National Renewable Energy Laboratory (NREL), in Boulder, Colorado. A 600 kW WT was equipped with rotor blades, developed, and manufactured within the SmartBlades2 research consortium. These blades were intensively equipped with instrumentation. In addition to this, a SpinnerLidar was installed on top of the turbine, to capture the incoming wind field with high resolution. The high-resolution measurement of rotor blade deformation and torsion using DIC, combined with the spatially and temporally detailed capture of the incoming wind field via SpinnerLidar, represents a unique approach. In summary, 13 measurement series are evaluated, covering a total measurement duration of 45.3 min on four different days. Based on this setup, DIC measurements are verified through comparative measurements. This marks the first time that DIC is verified for field application on WTs. An aeroelastic simulation model is established using OpenFAST. To enable a validation based on DIC measurements in the range of minutes, the simulations must closely replicate real-world conditions. Thus, a method is developed to directly feed in as much wind measurement data as possible. This feed-in method is verified with comparative wind measurement techniques in the field. The simulation model and the feed-in method are used to conduct transient post-test simulations of the measurement series that are evaluated with DIC. A validation of the WT behavior as well as the rotor blade deformation and torsion is carried out and evaluated. In the end, suggestions for improvements are given to further develop the already high potential of DIC for the future development of WTs.