In floating wind turbines, wind and wave excitation leads to motions of the floater that affect the rotor aerodynamic loads, which in turn influence the motion of the floater, in a highly coupled way. Numerical design tools can sometimes fail to predict certain aerodynamic phenomena, and therefore experimental testing is essential for tuning and validating these codes. Hybrid testing in wind tunnels, by measuring aerodynamic loads on a physical scale rotor under high-quality wind while numerically reproducing and actuating the floater motions, allows for higher fidelity in the reproduction of the aerodynamics compared to traditional wave basin tests. This work presents the development of a hybrid hardware-in-the-loop setup designed to study the aerodynamic response of floating wind turbines in wind tunnels. A scale model of a multi-megawatt floating wind turbine is mounted on top of a 6-degree-of-freedom hexapod robot. The full coupling of aerodynamic and floater dynamics is obtained with a hardware-in-the-loop approach with force-feedback–motion-actuation architecture. The rotor loads measured on the physical rotor are fed into a floater numerical simulator, which calculates the motion in real time and actuates it through the hexapod. Key outcomes include the development of a hardware-in-the-loop numerical model with an aerodynamic load estimation method to cope with scaling effects and the assessment of the floater simulator, the force estimation, and the measurement-actuation chain. The aerodynamic effects on the motion response are preliminarily investigated on a 10 MW floating concept, allowing the increase in pitch, yaw, and surge damping to be quantified through measured loads. The capability of testing combined wind and wave cases is also demonstrated, setting the framework for future studies. ... Read more

The rotor of a floating wind turbine is subject to complex aerodynamics due to changes in relative wind speeds at the blades and potential local interactions between blade sections and the rotor near wake. These complex interactions are not yet fully understood. Lab-scale experiments are highly relevant for capturing these phenomena and provide means for the validation of numerical design tools. This paper presents a new wind tunnel experimental setup able to study the aerodynamic response of a wind turbine rotor when subjected to prescribed motions. The present study uses a 1:148 scale model of the DTU 10 MW reference wind turbine mounted on top of a 6 degrees of freedom parallel kinematic robotic platform. Firstly, the thrust variation of the turbine is investigated when single degree of freedom harmonic motions are imposed by the platform, with surge, pitch and yaw being considered in this study. For reduced frequencies greater than 1.2, it is found that the thrust variation is amplified by up to 150 % compared to the quasi-steady value when the turbine is subject to pitch and surge motions, regardless of the amplitude of motion. A similar behaviour is also noticed under yaw motions. Secondly, realistic 6 degrees of freedom motions are imposed by the platform. The motions are derived from FAST simulations performed on the full-scale turbine coupled with the TripleSpar floater, and the tests aim at exploring the thrust force dynamics for different sea states and wind conditions, obtaining reasonable agreement with the simulations. Finally, the work shows the capabilities of an off-the-shelf hexapod to conduct hybrid testing of floating offshore wind turbines in wind tunnels, as well as its limitations in performing such tests. ... Read more

The rotor of a floating offshore wind turbine experiences intricate aerodynamics due to significant motion in the floating foundation, necessitating a holistic understanding through a synergistic blend of experimental and numerical methodologies. This study investigates rotor loads and the emergence of unsteady phenomena for a floating offshore wind turbine under motion. The approach compares a wind tunnel experimental campaign on a moving scale model with large-eddy simulations. Importantly, both experimental and numerical setups were co-designed simultaneously to match conditions and allow a fair comparison. The experimental setup features a 1:148 scale model of the DTU 10MW reference wind turbine on a six degrees of freedom robotic platform, tested in a wind tunnel. Numerically, the LES code YALES2, employing an actuator line approach undergoing imposed motions, is used. Harmonic motions on one degree of freedom in surge and pitch directions are explored at various frequencies. Thrust force variation aligns with quasi-steady theory for both numerical and experimental results at low frequencies. However, higher frequencies reveal the rise of unsteady phenomena in experiments. Large-eddy simulations, coupled with an actuator line approach, provide additional insights into the near- and mid-wake response to imposed motions. This co-design approach between numerical and experimental tests enhances the comprehension of aerodynamic behaviour in floating offshore wind turbines, offering valuable insights for future designs. ... Read more

The present paper describes the experiences gained from the design methodology and operation of a 3D physical model experiment aimed to investigate the dynamic behaviour of a spar buoy (SB) off-shore floating wind turbine (WT) under different wind and wave conditions. The physical model tests have been performed at Danish Hydraulic Institute (DHI) off-shore wave basin within the European Union-Hydralab+ Initiative, in April 2019. The floating WT model has been subjected to
a combination of regular and irregular wave attacks and wind loads. ... Read more