| 09 Sep 2025
How accurately do engineering methods capture floating wind turbine performance and wake? A multi-fidelity perspective
Abstract. 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 IEA's 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. Differently from previous studies, however, many more different operating conditions have investigated, including surge, pitch, yaw and wind-wave misalignment cases; moreover, numerical methos 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 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, up to 5D and in the operating conditions tested, platform motion has limited impact on the wake in terms of wake deficit. However, significant velocity oscillations are observed at a platform reduced frequency of 0.6 which could be detrimental for downstream machines. An investigation of the vortex structures in the wake showed that these velocity oscillations might be caused by the interaction of vortex structures generated under sinusoidal platform motion rather than by unsteady aerodynamic response of the rotor. FVW methods, if properly tuned, can correctly capture the wake response up to 3D from the rotor, but to simulate the wake response up to 5D, higher-fidelity methods are required. Significant improvements are achieved with ALM CFD simulations, even though an URANS approach might struggle to correctly predict the wake dissipation due to the interaction between the free-stream turbulence and wake.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Wind Energy Science.
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The manuscript by Cioni et al. (10+ authors) presents a comparative study of numerical simulation methods for analyzing floating wind turbine wakes. Two established simulation approaches—Free Vortex Wake and ALM-URANS—are employed to generate wake data, which are then compared against experimental results up to 5 rotor diameters downstream of a model wind turbine with prescribed motion. The authors also utilize blade-resolved URANS and ALM-LES methods on two cases to provide additional insights. The comparison reveals varying levels of agreement and discrepancies between simulated and experimental wake characteristics.
Overall, this reviewer finds the manuscript valuable to the floating wind energy research community, and the experimental data presented is particularly interesting. However, the manuscript contains numerous errors, including typographical mistakes, incorrect citations, erroneous section numbers, and disordered figure arrangements. The overall quality falls short of standard expectations for a submitted manuscript and appears more akin to a first draft. Nevertheless, these issues can be addressed through careful revision.
Given the number of errors identified, I hope the editor allows me to provided direct annotations on the PDF file of the preprint, with 70+ comments in total. I request that the authors carefully consider each annotation, provide point-by-point responses, and resubmit the manuscript for a second round of review.