Dynamics of floating wind turbine wakes in a wind tunnel setup

Amaral, Ricardo; Houtin-Mongrolle, Felix; von Terzi, Dominic; Laugesen, Kasper; Deglaire, Paul; Viré, Axelle

doi:10.5194/wes-2025-264

Preprints

https://doi.org/10.5194/wes-2025-264

Preprints

04 Dec 2025

| 04 Dec 2025

Status: this preprint is currently under review for the journal WES.

Dynamics of floating wind turbine wakes in a wind tunnel setup

Ricardo Amaral, Felix Houtin-Mongrolle, Dominic von Terzi, Kasper Laugesen, Paul Deglaire, and Axelle Viré

Abstract. The wake of a laboratory-scale wind turbine model is investigated in high-detail in a wind tunnel setup under prescribed surge, sway, roll, pitch, yaw and coupled surge-pitch motions using large-eddy simulations coupled to an actuator-line model. The goal is to assess how the wake of a moving turbine evolves in a high blockage ratio scenario and how it compares with the results found in the literature for full-scale models and experiments. This manuscript also extends the state-of-the-art to more degrees-of-freedom. Two cases per degree-of-freedom are considered: one with a low Strouhal number St and high normalized amplitude A^*, and vice versa. Cases with low-St/high-A^* exhibit a wake behavior similar to the fixed-bottom case. Conversely, cases with a high-St/low-A^* disturb the wake to a much larger extent. The contrast is caused by differences in how much the wake amplifies the perturbations of the floating motion upstream and is particularly noticeable at the blade tip and root trails. Prescribed motions with a component perpendicular to the flow are found to have a larger impact than motions exclusively in the flow direction. Overall, the phenomena found in the literature are well captured in this setup.

Received: 25 Nov 2025 – Discussion started: 04 Dec 2025

Competing interests: The authors have the following competing interests: RA, DvT and AV declare that they have no conflict of interest. FHM, KL and PD declare that they were full-time employees of Siemens Gamesa Renewable Energy at the time this work was carried out.

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.

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Ricardo Amaral, Felix Houtin-Mongrolle, Dominic von Terzi, Kasper Laugesen, Paul Deglaire, and Axelle Viré

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RC1:
'Comment on wes-2025-264', Anonymous Referee #1, 13 Jan 2026
Dear Authors,
I was invited by the Associate Editor to review your manuscript and was pleased to accept, as the topic is of strong interest to me and closely aligned with my recent research activities. In recent years, the wind energy community has shown increasing interest in the aerodynamics and wake interactions of floating wind farms, making the subject of this manuscript timely and potentially relevant to the readership of Wind Energy Science.
The results presented contribute to the growing body of research produced by several research groups in this area. While the findings are interesting, it would be beneficial to more clearly position them within the existing literature. In particular, the manuscript should better clarify whether the results are novel, whether they represent a complementary investigation of previously studied phenomena, and to what extent they agree or differ from existing studies. This contextualization is not always sufficiently clear in the current version.
Overall, I believe the manuscript is suitable to proceed in the review process at Wind Energy Science and may be considered for publication, provided that the authors adequately address the reviewers’ comments.
General comments
In several instances, the manuscript adopts a colloquial tone, with phrasing that is uncommon in research articles. A thorough language revision would improve clarity and ensure a more formal scientific style.

The study investigates the effect of platform motions in different directions on wake behavior, considering two reduced frequencies for each motion direction. In my opinion, this limited number of motion frequencies is insufficient to support generalized conclusions. Experimental and CFD studies conducted by multiple institutions have shown that wake response to rotor motion is strongly frequency dependent: the influence of motion typically increases with frequency up to a certain Strouhal number (often around St≈ 0.4, depending on the study) and then decreases as St tends toward infinity. This well-established behavior should be better acknowledged and reflected in the analysis.

The introduction does not clearly articulate how the present work differs from existing CFD studies of scaled floating wind turbines (for example [4], [5], [7], [8]). In particular, the manuscript should explicitly state what is novel in terms of the numerical approach, the motion conditions considered, and/or the wake analysis methodology.

The literature review and discussion of wake dynamics are generally well developed. However, an important body of related work is missing. The turbine and experimental setup investigated in this study have recently been the subject of additional wind tunnel experiments and correlated CFD simulations aimed at improving the understanding of wake dynamics, including motion directions not covered in the UNAFLOW campaign ([2], [3], [4], [7], [8]). While I am not requesting the addition of citations, it would be intuitive and appropriate to acknowledge the existence of this related work in order to better position the present study.

Specific comments
“One way of maximizing …”. I don’t want to change the cut of this study but i think that at this stage is more important (and safe) to understand the impact of motions, and design choices, on the energy in a floating wind farm. Designing floating wind turbine to excite wakes seems very far away.

L85: “No tower, nacelle … DOFs”. I understand the meaning but this sentence needs to be rewritten because the components actually do not appear in the figure

L90: “since it was prescribed …”. Not clear, especially because you also consider motion due to platform rotations where the velocity is not the same for every point of the rotor.

L107: “This simplification … relatively low”. However, simulations have shown that this low value is sufficient to have noticeable differences with respect to purely laminar case. The authors should discuss the effects this simplification has on the results, also looking at other published work that specifically addressed this point.

Caption of Table 3: I suggest recalling the meaning of the acronyms in the table caption so to ease the reading of the table itself.

L120: “from the corresponding values of the DTU 10 MW”. Which corresponding values?

L123: “summing … surge and pitch cases”. This is not clear. Is it that you applied the surge and pitch together?

L126: “pairs for single-DOF surge and pitch were realistic”. Realistic compared to what? How did you compare. the amplitude of single-DOF harmonic motion to the (broadband) response of a floating wind turbine? Do you refer to the spectral amplitude? At which frequency?

L152: “there were difficulties on both sides”. Do you mean uncertainties in the experiment and numerical simulation?

The results section uses some complex metrics about the wake (e.g., the velocity perturbation amplification factor, the normalized standard deviation of the velocity magnitude.) I think it would be useful to briefly present here the subsections that follows and explain, at high level, which analysis are conducted in each of them and to which purpose.

L179: “These results suggest …”. As mentioned before, I think this conclusion come from the fact that only two frequencies were analyzed. I think it is difficult to generalize it.

L208: “to originate wake recovery excess…” Not clear.

L240: replaces “excesses” with variations or “increments”.

L250: “The link makes sense … experiment”. The sentence, and the mechanism that is hypothesized for the explanation are not clear.

L252: “the coupling … the wake”. This part of the sentence does not have any meaning (the coupling result into some coupling).

L265: what are the “reminiscent peaks”?

L279: “this frequency range … was found”. Can you relate this conclusion to other studies on wake evolution of floating wind turbines (numerical or experimental)?

L298: “amplification potential”. In terms of lateral motion of the wake but i think the metric you have studied does not assess the amplification in the streamwise direction which corresponds to pulsing of the streamwise velocity.

L303: “Still, did this …”. Avoid rhetorical questions and give answers instead.

L317: “long lived” clarify that this means the vortices are found further downstream.

L323: “since defining the shear layer …”. Can you be more explicit? the additional information is needed to understand what really your metric is.

L400: “in terms of wake recovery…”. this sentence is poorly written, and the second part repeats the first one.

L405: “If the wake recovery … recovery”. This sentence is speculation. Reframe it or remove it.

L426: “At this point …”. How this conclusion relates to those of other research efforts on the same topic? Is it completely new? Does it agree or not?

L433: “The patterns …” Rewrite this sentence.

L445: “The wake meandering…” This sentence is not clear.

L478: “The prescribed motion …” Show them or remove this sentence.

L571: “Differences between the simulation setup …”. All these effects were introduced one by one in the simulations during OC6 [1], where most of the participants obtained a mean thrust close to 35N using a laminar inflow. I think the error of around 1N with respect to the results of OC6 could be related to the modelling of the boundary layer of wind tunnel walls. Assuming the boundary layer grows of 0.01m every going downstream the tunnel chamber, the boundary layer on every wall is around 0.2m at the turbine location. This affects the flow velocity that accelerate in the center of the tunnel, and this can explain the slightly lower mean thrust that was obtained here. I cannot comment on other uncertainties introduced by the simulation tools itself (like calculation of angle of attack along the actuator lines).

Technical corrections
L1: “in a wind tunnel setup” is redundant.

L84: add “used in the CFD simulations” after “The turbine configuration”.

L133: “larger” -> “longer (in the wind direction)”.

L147: I suggest c_\mathrm{CFL} in place of “CFL” otherwise it seems C*F*L.

L227: replace “TI” with “I_i” or “I_x”.

L238: replace “side to side” with cross stream?

L316: replace “merger” with “merging”.

L359: “are” is missing between “paper” and “well”.

L485: “Appendix A: Prescribed motion validation”. I think this is more a verification of the blade kinematics in the simulation.

L570: “Appendix C2 Discussion”. It's unusual to have sections in appendix.

References
[1] Bergua, R., Robertson, A., Jonkman, J., Branlard, E., Fontanella, A., Belloli, M., Schito, P., Zasso, A., Persico, G., Sanvito, A., Amet, E., Brun, C., Campaña-Alonso, G., Martín-San-Román, R., Cai, R., Cai, J., Qian, Q., Maoshi, W., Beardsell, A., Pirrung, G., Ramos-García, N., Shi, W., Fu, J., Corniglion, R., Lovera, A., Galván, J., Nygaard, T. A., dos Santos, C. R., Gilbert, P., Joulin, P.-A., Blondel, F., Frickel, E., Chen, P., Hu, Z., Boisard, R., Yilmazlar, K., Croce, A., Harnois, V., Zhang, L., Li, Y., Aristondo, A., Mendikoa Alonso, I., Mancini, S., Boorsma, K., Savenije, F., Marten, D., Soto-Valle, R., Schulz, C. W., Netzband, S., Bianchini, A., Papi, F., Cioni, S., Trubat, P., Alarcon, D., Molins, C., Cormier, M., Brüker, K., Lutz, T., Xiao, Q., Deng, Z., Haudin, F., and Goveas, A.: OC6 project Phase III: validation of the aerodynamic loading on a wind turbine rotor undergoing large motion caused by a floating support structure, Wind Energ. Sci., 8, 465–485, https://doi.org/10.5194/wes-8-465-2023, 2023.
[2] Fontanella, A., Fusetti, A., Cioni, S., Papi, F., Muggiasca, S., Persico, G., Dossena, V., Bianchini, A., and Belloli, M.: Wake development in floating wind turbines: new insights and an open dataset from wind tunnel experiments, Wind Energ. Sci., 10, 1369–1387, https://doi.org/10.5194/wes-10-1369-2025, 2025.
[3] Fontanella, A., Cioni, S., Papi, F., Muggiasca, S., Bianchini, A., and Belloli, M.: Experimental investigation of the effects of ﬂoating wind turbine motion on a downstream turbine performance and loads, Wind Energ. Sci. Discuss. [preprint], https://doi.org/10.5194/wes-2025-106, in review, 2025.
[4] Pagamonci, L., Papi, F., Cojocaru, G., Belloli, M., and Bianchini, A.: How does turbulence affect wake development in floating wind turbines? Some insights from comparative large-eddy simulations and wind tunnel experiments, Wind Energ. Sci., 10, 1707–1736, https://doi.org/10.5194/wes-10-1707-2025, 2025.
[5] Mian, H. H., Messmer, T., Stoevesandt, B., and Siddiqui, M. S.: Coherent flow structures in the wake of a model floating wind turbine under pitch and roll motions. Energy, Volume 335, https://doi.org/10.1016/j.energy.2025.138212, 2025.
[6] Messmer, T., Peinke, J., Croce, A., and Hölling, M.: The role of motion-excited coherent structures in improved wake recovery of a floating wind turbine, Journal of Fluid Mechanics. 1018:A23. https://doi.org/10.1017/jfm.2025.10509, 2025.
[7] Cioni, S., Francesco, P., Balduzzi, F., Fontanella, A., and Bianchini, A.: Blade-resolved CFD analysis of a floating wind turbine: new insights on unsteady aerodynamics, loads, and wake. Ocean Engineering, Volume 341, Part 3, https://doi.org/10.1016/j.oceaneng.2025.122746, 2025.
[8] Firpo, A., Sanvito, A. G., Persico, G., and Dossena, V.: Multi-fidelity actuator line modelling of tandem floating offshore wind turbines, Wind Energ. Sci. Discuss. [preprint], https://doi.org/10.5194/wes-2025-194, in review, 2025.
Citation: https://doi.org/10.5194/wes-2025-264-RC1
RC2:
'Comment on wes-2025-264', Anonymous Referee #2, 09 Apr 2026
The manuscript investigates the dynamics of floating wind turbine wakes in a wind tunnel setup through numerical simulations. The authors simulate a downscaled wind turbine used in a wind-tunnel experimental campaign and extend it to include additional degrees of freedom. The study examines two sets of dynamic parameter combinations (amplitude and Strouhal number) for each type of motion, evaluating and comparing how different motions affect wake characteristics.
In my opinion, the topic itself is interesting; however, I am quite confused about the rationale and motivation for simulating a downscaled turbine in a wind tunnel (with limitations such as confined space and blockage effects) and under such low turbulence intensity conditions. This setup makes the results less relevant to real-world applications. Moreover, the choice of only two sets of dynamic parameter combinations is insufficient to represent wake dynamics or to justify trends within a given parameter range (unless supported by rigorous theoretical arguments). In addition, thorough proofreading is strongly recommended to improve readability and clarity.
My specific comments are provided as follows.
Introduction:
The introduction lacks coverage of recent studies on wind tunnel experiments (e.g., involving single- or multiple-degree-of-freedom motions), as well as numerical or experimental investigations under high-turbulence-intensity or atmospheric boundary layer (ABL) conditions. It should be more comprehensive, given the topic under investigation.

The knowledge gaps are not clearly identified, and the novelty and contributions are not well articulated. The rationale for selecting only two sets of Strouhal number–amplitude (St–A*) combinations, as well as the use of such a low turbulence intensity, is not explained. The definitions of St and A* should also be provided upon first use.

Methodology

Line 77: Details of the wind tunnel should be provided.

Line 83: The power coefficient (Cp) and thrust coefficient (Ct) of the turbine model should be reported, along with details of the operational and control strategies applied.

Lines 106–107: What is the rationale for using such a low and unrealistic turbulence intensity? Is the inflow sheared? If the goal is to isolate the pure effects of motion, why not use laminar inflow instead?

Parameter selection: Why were only two parameter pairs selected for each motion? What representative operating conditions do these pairs correspond to? The selection omits intermediate Strouhal numbers that may lead to different wake dynamics. Moreover, is it realistic for low-frequency motions to be associated with large amplitudes?

Line 135: If wall shear and turbulence are present, the inflow profiles of mean velocity and turbulence intensity should be provided. In the experimental setup, the turbine top appears to be very close to the wind tunnel ceiling. How does this proximity affect wake dynamics? Is this effect accounted for in the precursor inflow simulation? Please comment on how representative this setup is compared to more realistic conditions (e.g., absence of a ceiling boundary layer and lower blockage effects).

Line 155: How is the rotational speed regulated? Is it dynamically adjusted or kept constant? How realistic is this approach?

Results
Lines 179–183: Can the authors provide a physical interpretation of the observed behavior?

Lines 201–202: What explains the significant difference observed at x* = 3? Is this consistent with findings reported in the literature? Could this discrepancy be due to domain confinement in the wind tunnel and the absence of a fully developed wake region in the simulations?

Line 220: What is meant by “destabilization of the inner jet”? How reliable is it to explain wake recovery based on instantaneous wake velocity alone? What role does ambient turbulence play in this context?

Lines 247–249: This sentence is difficult to follow and should be clarified.

Section 3.5 (Wake meandering): Can the authors comment on how wake meandering might differ under realistic atmospheric boundary layer conditions?

Discussion & Conclusion
These sections should explicitly identify the limitations of the present study and discuss how the results might differ under realistic inflow conditions and across a broader range of dynamic parameters.
Citation: https://doi.org/10.5194/wes-2025-264-RC2

Ricardo Amaral, Felix Houtin-Mongrolle, Dominic von Terzi, Kasper Laugesen, Paul Deglaire, and Axelle Viré

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Short summary

This work uses simulations to investigate floating wind turbines which have the potential to supply the world's electricity demand many times by 2040. In particular, the effect of the rotor motion was investigated on the wake by forcing the turbine to move under a variety of motions. The results highlight differences in the effect of these motions. While some led to a wake behavior that was close to that of a fixed-bottom turbine, other motions produced a remarkably different wake structure.


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