the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 15 Oct 2025
Phase-controlling the motion of floating wind turbines to reduce wake interactions
Abstract. The wake interaction between wind turbines causes significant losses in wind farm efficiency that can potentially be alleviated using wake control techniques. We provide detailed experimental evidence on how the coupling between the so-called Helix wake control technique and a floating turbine's yaw dynamics can be used to increase wake recovery. Using tomographic particle image velocimetry during wind tunnel experiments, we analysed the wake dynamics and its coupling to a floating wind turbine. The measurements show that ensuring the floating turbine's yaw motion is in phase with the blade pitch dynamics of the Helix technique enables an increase of 12 percentage points in available energy in the flow on top of the Helix method applied to bottom-fixed turbines. We find that the in-phase scenario results in an earlier interaction between tip and hub vortex inside the wake, which leads to the desired breakdown of it, thus accelerating the energy advection into the wake.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Wind Energy Science.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
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Status: final response (author comments only)
- RC1: 'Comment on wes-2025-201', Anonymous Referee #1, 01 Nov 2025
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RC2: 'Comment on wes-2025-201', Anonymous Referee #2, 19 Nov 2025
The paper presents a wind tunnel experiment investigating how the yaw motion of the floater of a floating offshore wind turbine affects wake recovery when combined (or not combined) with HELIX wake control.
The paper is well written, and the study is highly relevant to the wind energy community, as it addresses the important topic of wind turbine wake control.
Therefore in the reviewer’s opinion it deserves publication to WES after the following listed points are addressed.
1) An important consideration in wind-tunnel wake measurements is the influence of ambient turbulence. In the present experiment, the ambient turbulence level is relatively low (0.5%–2%), considerably lower than what is typically observed in the field. As a result, although the qualitative trends remain consistent, the quantitative conclusions may differ under real conditions, where higher ambient turbulence enhances and accelerates wake mixing. It is recommended to the authors to address this point in the introduction and perhaps in the conclusion section and discuss the limitations. Please indicate the lessons learned by the experiments you cite in the introduction section with regard to the above point.
2) Figure 2, which presents the frequency-response analysis of the realistic dynamic system of a floating offshore turbine, indicates that the phase difference between the pitch motion and the platform’s yaw motion is closer to 180 deg than to 0 deg. In contrast, the experimental results suggest that mixing is enhanced when the two motions are in phase. The frequency plots in Figure 2 represent the response of a dynamic system that cannot be subject (at least not easily) to modulation. Therefore, while it is interesting that in-phase motion appears to enhance mixing, it may be unrealistic to assume that such perfectly in-phase motion can occur in practice. Please comment on this issue.
3) A detailed wake measurement campaign was carried out, and it is unfortunate that the paper presents only the averaged cross-sectional wake velocities. It would be helpful if the authors included a plot showing the spatial variation of velocity within the wake, illustrating how the enhanced recovery observed in certain cases is distributed across the wake region. Such data could serve as benchmark results for validating numerical models. The pattern plots of figure 4 do not provide that necessary quantitative detail.
4) Please provide the formulas used to calculate the energy advection, along with details on how this quantity is computed.
5) For the sake of completeness and clarity, please indicate whether the picture in Fugure 1 is a schematic representation of the wake or a result of simulations and of what kind of simulations.
6) Please rephase the following sentence which is unclear (in Section 2, second sentence)
“The wind tunnel experiments are carried out that combine a hardware-in-the-loop setup and tomographic particle image velocimetry (PIV) to represent and measure the turbine dynamics, the coupled hydrodynamics, and the resulting aerodynamics.”
Citation: https://doi.org/10.5194/wes-2025-201-RC2
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The manuscript presents wind tunnel experiments on a dynamically yawing scaled wind turbine platform, designed to emulate the motion of a floating offshore turbine subjected to helix-type control inputs. The authors show that wake recovery is enhanced when the helix actuation is in phase with the yaw motion, and they provide an explanation based on vortex interaction mechanisms.
Overall, the paper is clearly written, the figures are of high quality, and the topic is timely and relevant to ongoing research in floating wind turbines and wake control. The results are novel and potentially valuable. However, before publication, several aspects—particularly regarding the physical modeling, scaling assumptions, and the description of the QBlade simulations—need clarification or expansion.
Below, I provide major points of discussion followed by specific comments where I refer to the lines of text in the preprint pdf.
I hope they can be useful to improve this work, and I look forward to see a new iteration.
Major Comments
The paper’s methodology relies heavily on simulated platform motions obtained with QBlade, which are then prescribed to the moving platform in the wind tunnel. Currently, this description is in the Appendix and lacks clarity. I strongly suggest moving this material into the main text and expanding it. In particular: the simulations use multi-megawatt rotors and realistic floating platforms. How are these motions scaled to the MoWiTo model? Please discuss the scaling laws (Reynolds, Froude) and justify whether dynamic similarity is preserved.
It appears that only yaw motion is modeled, while wave-induced and tilt motions are neglected. Please clarify whether this simplification is justified, and discuss its implications for the generality of the results.
The scaled turbine operates at an optimal TSR of 5, which is substantially lower than that of modern large turbines (typically 7–9). The paper should discuss how this affects the wake development and vortex dynamics.
In Fig. 7, the near-wake differences between in-phase and anti-phase cases are significant; however, with a higher TSR the near wake would likely contract and recover differently.
Similarly, the characterization of tip and root vortices (Fig. 8) should note that vortex strength and persistence depend on TSR.
The results could be strengthened by comparison with or validation against CFD simulations (e.g., LES ALM). Even a qualitative comparison would enhance the credibility of the wake structure analysis.
More specific comments:
- line 232: "a simulation suite capable of simulating", remove repetition
- line 234: what are OC4, TripleSpar, and VoltrunUS-S?
- line 261: Why is the future tense used here and later?
- lines 264, 265: lack of citations for "... these motions are significantly smaller than those excited by the Helix method itself.", and "the frequency of wave excitation is typically an order of magnitude higher than the application frequency of the Helix". These are rather important statements that require a citation or a discussion, in my opinion.