How accurately do engineering methods capture floating wind turbine performance and wake? A critical perspective using multi-fidelity simulations

Despite an increasing number of experimental and numerical studies, the influence of platform motion on wake dynamics (wake recovery and turbulence production) in floating offshore wind turbines is still an open research question. In particular, efforts are being made to understand the accuracy of numerical models in use so far for fixed-bottom turbines when they are applied to floating configurations. Similarly to what has been done in the IEA OC6 task, in this work, a multi-fidelity approach is leveraged to investigate the capabilities of engineering models to capture the wake dynamics of a wind turbine model under imposed motion. In contrast to previous studies, however, many more different operating conditions have been investigated, including surge, pitch, yaw, and wind–wave misalignment cases; moreover, numerical methods are here consistently applied to the same test cases, which are part of the first experimental round of the NETTUNO project. More specifically, free vortex wake (FVW), actuator line model (ALM), and blade-resolved computational fluid dynamics (CFD) simulations have been benchmarked, and their capabilities in predicting the mean wake response and the onset of velocity oscillations in the wake of a floating wind turbine were evaluated. Results showed that FVW methods, if properly tuned, can correctly capture the wake response up to 3 D from the rotor, but to simulate the wake response up to 5 D, higher-fidelity methods are required. Significant improvements are achieved with ALM CFD simulations, even though a URANS approach might struggle to correctly predict the wake dissipation due to the interaction between the free-stream turbulence and wake.