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https://doi.org/10.5194/wes-2025-135
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/wes-2025-135
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
20 Aug 2025
| 20 Aug 2025
Status: this preprint is currently under review for the journal WES.
Wind-tunnel analysis of wake-steering control strategies on a multi-column model wind farm
Abstract. Wake-steering control has the potential of improving the power production of wind farms by deflecting the wakes of upstream turbines away from the downstream ones, thereby increasing the velocity impinging on the latter by sacrificing the performance of the former. In this work, a wide range of wake-steering control strategies are systematically applied to a 3 × 3 wind farm in a series of wind-tunnel experiments. When each streamwise column is operated identically to the others, the maximum measured power gain is approximately 5.3 %. It is observed that the columns respond differently to a given yaw configuration, with the central one generally improving to a smaller degree than the lateral ones. Nevertheless, our data indicate that tuning each column independently of the others does not result in further power improvements. Furthermore, we show that increasing the free-stream velocity enhances the baseline power production of the model farm but reduces the scope for improvement achievable with wake-steering control.
How to cite. Micheletto, D., Fransson, J., and Segalini, A.: Wind-tunnel analysis of wake-steering control strategies on a multi-column model wind farm, Wind Energ. Sci. Discuss. [preprint], https://doi.org/10.5194/wes-2025-135, in review, 2025.
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RC1: 'Comment on wes-2025-135', Anonymous Referee #1, 21 Sep 2025
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The manuscript investigates yaw configurations in a 3×3 turbine array exposed to a sheared, turbulent inflow in a wind tunnel. The dataset is extensive and carefully obtained, with clear attention to ensuring realistic inflow conditions. In general, the manuscript is well-written, interesting, mostly easy to follow, and well-situated within the existing literature.However, the following issues, two of them major, require clarification before publication.Major concerns1. Representation of an infinite wind farm through wall proximityLines 194–195: I disagree with the claim that the presented setup resembles an infinite wind farm. The lateral turbine columns are positioned very close to the solid wind tunnel walls. This proximity likely constrains the natural wake expansion of an uncontrolled wake and artificially limits wake deflection under yaw. This raises the following questions and concerns about the validity of several conclusions:1.1 What is the blockage ratio of the setup?1.2 If the setup were representative of an infinite wind farm, why do the left and right columns react differently to yawing of the first row turbine (lines 291 ff.)? In an infinite wind farm, all columns should behave equally.1.3 Section 3.1.3 (particularly lines 331–333) contradicts the infinite-farm hypothesis. The authors state that lateral columns benefit from lateral entrainment, yet by definition in an infinite wind farm lateral entrainment does not exist, because each column is neighbored by two other column.1.4 In Fig. 18, why does the relative performance of the columns change so strongly with wind speed (e.g., the center column is the worst at 7 m/s but the best at 8 m/s)? Could this be an artifact of blockage and local acceleration effects from insufficient spacing to the tunnel walls?The conclusions would be significantly strengthened if the influence of the side walls were assessed, for example, by repeating experiments with only a single turbine column placed at left, center, and right positions. This would clarify the wall’s impact, especially when wakes are steered toward it.2. Asymmetry in yaw steering performanceThe asymmetry in power generation between positive and negative yaw angles (Fig. 7) is surprising and highly relevant for ongoing research and recent efforts in commercial deployment of wake steering. If wake steering benefits only from one yaw direction, the concept itself requires reevaluation. This point needs more careful discussion:2.1 Lines 277–282: The authors attribute the asymmetry to lower tip speed ratio compared to real turbines, causing enhanced wake swirl. To what extent do these results translate to utility-scale turbines? Should we expect directional dependence of yaw steering benefits in practice?2.2 How sensitive is this asymmetry to inflow conditions? Would a differently sheared inflow produce the same result?2.3 Fig. 11c: The proposed explanation of the linear trend due to vertical wake displacement is not convincingly demonstrated. Can this be substantiated with wake measurements or LES?Further concerns3. Graphical presentation3.1 Several figures use the label “config Nr” on the x-axis. While interesting trends are presented, this label does not convey the underlying physical parameter being varied, making interpretation difficult. Replacing “config Nr” with a meaningful physical variable would improve clarity.3.2 Many results are shown as scatter plots with both marker color and shape encoding additional variables. This creates very dense visualizations where trends are difficult to see. Moreover, continuous colormaps for discrete yaw angles are confusing. Alternative formats, such as contour plots with the row-wise yaw angles on x- and y-axes, and performance metrics (Cp, thrust, etc.) as a colormap, may more clearly highlight the trends. Additionally, varied parameters (e.g., γ3) could be separated into dedicated subplots.Minor commentsLine 3: “wide range of wake steering control strategies” is vague; consider “wide range of yaw steering configurations in a wind farm.”Line 40: The abbreviation “LES” should be defined.Fig. 6: Why is Cp,opt=0.325 so much lower than the Betz limit of 0.593?Line 147: The use of gradient-based optimization for each yaw setting makes sense scientifically, but how realistic is this for actual wind farm operation? Could comparable methods be applied in practice?Fig. 14: Appears redundant with Fig. 13, given the correlation between power and thrust.This study addresses a relevant topic, and the dataset has significant value. However, before acceptance, the concerns outlined above—particularly regarding wind tunnel wall effects and yaw asymmetry—must be resolved.ReplyCitation: https://doi.org/
10.5194/wes-2025-135-RC1
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FLOW, Dept. Eng. Mech., KTH Royal Institute of Technology, Stockholm, Sweden
Jens Fransson
FLOW, Dept. Eng. Mech., KTH Royal Institute of Technology, Stockholm, Sweden
Antonio Segalini
Dept. Earth Sci., Geocentrum, Uppsala University, Uppsala, Sweden
Short summary
We conducted wind-tunnel experiments on 9 wind turbine models and measured their power while intentionally yawing them away from the wind direction. By testing a broad range of yaw-angle combinations, we found that this method can increase the total power output by up to 5.3 %. We also observed how different columns of turbines respond uniquely to these changes and how wind speed affects the overall improvement. Our findings could be useful in developing more accurate wind-farm control models.
We conducted wind-tunnel experiments on 9 wind turbine models and measured their power while...
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