On the development of a hardware-in-the-loop wind tunnel setup to study the aerodynamic response of floating offshore wind turbines

Abstract. In floating wind turbines, the met-ocean conditions lead to motions of the floater affecting the rotor aerodynamic loads, which in return influence the motion of the floater, in a highly coupled way. Numerical design tools have proven to fail to predict some aerodynamic phenomena, such as the increase in thrust variation caused by unsteady effects. Thus, experimental testing is essential for tuning and validating these codes. Hybrid testing in wind tunnels, by reproducing numerically and actuating the floater motions while measuring aerodynamic loads on a physical scale turbine model, overcomes the scaling issues of traditional wave basin tests allowing a higher fidelity in the reproduction of the aerodynamics. 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 six degrees-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 dynamic numerical simulator which calculates the motion in real-time and actuates it through a moving platform called hexapod. Key outcomes include the development of a hardware-in-the-loop numerical model with a force correction method to cope with scaling effects and an assessment procedure to verify the simulator, correction model, and measurement-actuation chain. The aerodynamic effects on the motion response are preliminarily investigated on a 10 MW floating concept, with direct estimation of the rotor aerodynamic damping showing a 210 % increase of damping in pitch with the turbine in operation. The capability of testing combined wind and wave cases is also demonstrated, setting the framework for future studies.