the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 07 Oct 2025
Multi-fidelity actuator line modelling of tandem floating offshore wind turbines
Abstract. The motion of floating offshore wind turbine platforms strongly affects wake development, influencing energy production, farm layout, and turbine loads. Unlike fixed-bottom turbines, floating turbine wake interactions are less understood and require high-fidelity modeling. This study employs an Actuator Line Model approach to investigate two turbines, with the upstream platform undergoing surge and pitch motions. Multi-fidelity simulations (URANS, LES with laminar and turbulent inflow) are performed to separate the effects of platform motion and inflow turbulence on wake dynamics and to assess URANS capability in capturing floating turbine wakes. Simulations of the single floating turbine are validated against experimental load and wake data. Wake validation shows that LES with turbulent inflow best captures turbulence intensity distribution, while URANS reproduces mean velocity profiles accurately especially in the near-wake. Platform motion enhances wake recovery under laminar inflow, whereas under turbulent inflow the wake recovers faster and the effect of motion is reduced; URANS shows slower far-wake recovery compared to turbulent LES. Analysis of platform-motion-induced wake oscillations indicates that turbulent LES accurately reproduces amplitudes, while URANS underestimates them and laminar inflow LES is inadequate. Furthermore, no significant differences is found between surge and pitch cases. Wake meandering is found to be primarily driven by turbulent inflow rather than platform motion: turbulent LES captures wake displacement at a characteristic frequency, whereas URANS fails to reproduce it. The impact of the wake on a downstream turbine 5D away is finally assessed and reveals that URANS underestimates both mean values and amplitudes of the downstream turbine loads. Blade distributed load analysis shows that URANS captures platform-motion-induced variability upstream but misses turbulence-driven effects downstream. In conclusion, this study provides a detailed characterization of floating turbine wake dynamics, highlights the different accuracy of LES and URANS, and demonstrates that LES yields more reliable predictions of downstream turbine loads, essential for their structural assessment within wind farms.
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Status: closed
- RC1: 'Comment on wes-2025-194', Anonymous Referee #1, 20 Nov 2025
- RC2: 'Comment on wes-2025-194', Anonymous Referee #2, 25 Nov 2025
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AC1: 'Comment on wes-2025-194', Giacomo Persico, 22 Dec 2025
The Authors would like to thank the Editor and the Reviewers for the evaluation of the draft version of the paper and for their relevant and constructive remarks and suggestions, which have considerably helped us in improving the paper through a significant revision.
In the attached file, the Authors provide detailed answers and comments to all the remarks raised by both the referees, also highlighting the revisions made to the paper to match their recommendations.
Status: closed
-
RC1: 'Comment on wes-2025-194', Anonymous Referee #1, 20 Nov 2025
The manuscript “Multi-fidelity actuator line modelling of tandem floating offshore wind turbines” by Firpo et al. documents a numerical study on how flow simulation methods at different levels of fidelity (URANS, LES) impact the wake of a floating wind turbine modelled by actuator line methods. The impact of the wake on the loads of a second wind turbine placed downstream is also investigated. The paper confirms many known phenomena, such as that inflow turbulence reduces the difference between the wakes of a fixed and a floating wind turbine, and that LES is better than URANS when simulating wake dynamics. This manuscript could be considered for publication if the following comments are taken into account.
- My main concern is about the title of the manuscript. Conventionally, “multi-fidelity” modelling refers to simulation methods that employ models at different levels of fidelity simultaneously and consider information exchange at the interfaces between these models. However, this work compares URANS and LES without coupling them together in the same simulation. This cannot be referred to as multi-fidelity.
- My second concern is also about the title. The focus of the work is mostly on the wake of a single floating wind turbine. It is only in Section 6 that the second wind turbine is introduced; only one of seven sections concerns the tandem configuration, so I don’t think the title emphasizing tandem configuration is appropriate.
- The reason why URANS cannot reproduce large coherent structures should be studied in more depth. In principle, these large structures should not be so difficult to predict. Please verify whether the same phenomenon still occurs if the URANS employs the same grid as LES.
- It is found that the inflow triggers significant meandering in the wake. The spatial and temporal scales are very important to the receptivity of the wake. In Figure A1(b), the low-frequency peak of the experimental data and of the simulations differ considerably. Please try to see whether this discrepancy persists if a different inflow turbulence is employed.
Some point comments are:
- Line 191, please specify how the Courant number is defined. If it is defined based on the flow velocity, then the rotor tip, traveling much faster than the local flow, could cross many grid cells in a single time step.
- Figure 3, it is suggested to add a subplot for the LES_laminar case as well.
- The captions of the figures are not self-contained. It is not clear what the light-colored curves represent.
- Line 400, it is odd that a work published in 2024 is said to be confirmed by a work published in 2022.
Citation: https://doi.org/10.5194/wes-2025-194-RC1 - RC2: 'Comment on wes-2025-194', Anonymous Referee #2, 25 Nov 2025
-
AC1: 'Comment on wes-2025-194', Giacomo Persico, 22 Dec 2025
The Authors would like to thank the Editor and the Reviewers for the evaluation of the draft version of the paper and for their relevant and constructive remarks and suggestions, which have considerably helped us in improving the paper through a significant revision.
In the attached file, the Authors provide detailed answers and comments to all the remarks raised by both the referees, also highlighting the revisions made to the paper to match their recommendations.
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The manuscript “Multi-fidelity actuator line modelling of tandem floating offshore wind turbines” by Firpo et al. documents a numerical study on how flow simulation methods at different levels of fidelity (URANS, LES) impact the wake of a floating wind turbine modelled by actuator line methods. The impact of the wake on the loads of a second wind turbine placed downstream is also investigated. The paper confirms many known phenomena, such as that inflow turbulence reduces the difference between the wakes of a fixed and a floating wind turbine, and that LES is better than URANS when simulating wake dynamics. This manuscript could be considered for publication if the following comments are taken into account.
Some point comments are: