the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 13 Nov 2025
Multi-Scale Mapping of Sectional Stiffness Coupling in IEA 10MW,15 MW, and 22 MW Wind-Turbine Blades
Abstract. This study compares the spanwise stiffness and stiffness coupling characteristics of 10 MW, 15 MW, and 22 MW wind turbine blades using sectional 6×6 stiffness matrices extracted from NREL BeamDyn_blade input files. We define a normalized coupling coefficient and a root-mean-square (RMS) coupling score to map how axial–bending, shear–torsion, and bending–torsion interactions evolve along the blade span. With increasing scale, the 10 MW blade shows strong, localized coupling “hotspots” inboard, the 15 MW blade redistributes these interactions across mid-span, and the 22 MW blade exhibits weaker peak coupling but broader spatial influence extending toward the tip. This “smoothing with scale” indicates a design shift away from highly localized passive load alleviation and toward globally distributed aeroelastic tailoring for ultra-long (>130 m) blades. The method is fully reproducible from public OpenFAST model inputs. These findings provide crucial insights for the structurally-optimized and aeroelastically-stable design of next-generation megawatt-scale turbines.
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Status: open (until 21 Jan 2026)
- RC1: 'Comment on wes-2025-230', Anonymous Referee #1, 29 Dec 2025 reply
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RC2: 'Comment on wes-2025-230', Anonymous Referee #2, 02 Jan 2026
reply
General Assessment:
The manuscript presents a comparative analysis of the full 6 x 6 sectional stiffness matrices of three reference wind turbine blades (10 MW, 15 MW, and 22 MW) with the stated aim of identifying scaling trends in stiffness coupling, particularly bend–twist coupling (BTC), for ultra-long blades. While the topic is potentially relevant, the current manuscript remains largely descriptive, lacks physical and aeroelastic interpretation, and does not convincingly demonstrate that the reported observations yield meaningful insight into blade upscaling or BTC-related design implications. Therefore, as the manuscript does not meet the scientific depth and rigor expected for publication in Wind Energy Sciencein its current form, I regret to say that I cannot recommend it for publication.
Major comments:
- Lack of physical interpretation and consequences of BTC
The manuscript does not clearly explain the direct consequences of bend–twist coupling in the context of ultra-long wind turbine blades. The potential advantages and disadvantages of BTC (e.g., load alleviation, aeroelastic stability, flutter margins, controllability) are neither discussed nor quantified. As a result, the reader is left without understanding why the reported coupling trends are important or how they affect blade performance.
- Incorrect and confusing presentation of the stiffness matrix coupling terms in Figures 4, 8, and 11
For a symmetric 6×6 stiffness matrix, there are only 15 independent off-diagonal coupling terms, yet Figures 4, 8, and 11 display 30 terms, effectively duplicating symmetric entries. This duplication is not explained and significantly complicates interpretation. This represents a serious presentation flaw, and it took considerable effort to realize that the results were repeated rather than distinct.
- Unclear link between stiffness coupling and upscaling
The manuscript itself states that each sectional stiffness matrix results from composite layups, fiber orientations, and thickness distributions, which are design choices, not purely scaling effects. Consequently, it is unclear whether the observed differences between the three reference turbines reflect upscaling trends or merely different design philosophies. Comparing only three reference turbines is insufficient to disentangle these effects.
- Speculative and unsupported interpretive statements
Several key claims are made without evidence or analysis, for example:
(i): "This redistribution signifies a maturation in structural tailoring.”
(ii): "Designers have successfully spread the coupling effects to achieve load alleviation benefits."
(III): "Smoothing of the coupling landscape is a critical evolutionary step for ultra-long blades."
These statements are speculative and are not supported by aeroelastic analysis, sensitivity studies, or design optimization results. Moreover, it is not demonstrated that “spreading the coupling” is beneficial, nor what trade-offs it introduces. - Weak and casual cross-scale comparison using the RMS coupling metric
The comparisons based on the “overall coupling score, K_RMS (s)" presented in Figures 7, 10, and 13, are not convincing. Several of the claimed differences are not evident from the plots, and the physical meaning of the RMS metric is not established. Without further analysis linking this metric to aeroelastic response or design outcomes, the comparison remains superficial. - Code availability claim is incorrect
The manuscript states that the analysis code is available. However, no code is provided or accessible. This contradicts the claims made under "code availability" and undermines the reproducibility of the study.
In its current form, the manuscript primarily reports stiffness matrix data of three reference turbines with minimal analysis. This level of reporting is insufficient for wind Energy Science, which typically requires mechanistic insight, sensitivity analysis, or demonstrated consequences for aeroelastic performance or design.
Recommendations for Improvement:
In my humble opinion, to make the manuscript suitable for future publication, the author should, at minimum achieve one of the points listed below:
- Conduct comparative or sensitivity studies similar to those in Refs. [1], [4], or Shakya et al. (2019, see below).
- Quantify the impact of coupling “hot spots” versus smooth coupling distributions on aeroelastic stability, flutter, or load response.
- Analyze a larger dataset of real turbine blades (at least ten) to support claims of scaling trends rather than relying on three reference designs that have never been realized.
- Clearly distinguish design-driven effects from scaling-driven effects.
Shakya, P., Sunny, M. R., & Maiti, D. K. (2019). A parametric study of flutter behavior of a composite wind turbine blade with bend-twist coupling. Composite structure, 207, 764-775.
The manuscript contains serious citation errors. Four of the seven references are incorrectly cited. These issues substantially undermine the credibility of the work and its engagement with the existing literature. See below:
- Ref. 2: Incorrect journal.
Correct citation:
Fedorov, V., & Berggreen, C. (2014). Bend–twist coupling potential of wind turbine blades. Journal of Physics: Conference Series, 524(1), 012035. - Ref. 3: Incorrect authors.
Correct citation:
Larwood, S., Van Dam, C. P., & Schow, D. (2014). Design studies of swept wind turbine blades. Renewable Energy, 71, 563–571. - Ref. 4: Incorrect authors and year.
Correct citation:
Li, B., Tian, D., Wu, X., Meng, H., & Su, Y. (2023). The impact of bend–twist coupling on structural characteristics and flutter limit of ultra-long flexible wind turbine composite blades. Energies, 16(15), 5829. - Ref. 5: Incorrect authors.
Correct citation:
Canet, H., Bortolotti, P., & Bottasso, C. L. (2021). On the scaling of wind turbine rotors. Wind Energy Science, 6(3), 601–626. - References 6 and 7 are conceptually correct but poorly formatted.
I hope these comments will be helpful to the author in improving this manuscript and in guiding future work.
Best
Citation: https://doi.org/10.5194/wes-2025-230-RC2 - Lack of physical interpretation and consequences of BTC
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Dear Author,
Thank you for your submission. I greatly appreciated the effort spent in documenting your studies and I enjoyed reviewing your work. Unfortunately, in its current form, I do not think that the manuscript meets the scientific standards required by the journal Wind Energy Science.
I agree with the author that modern 100m+ blade designs require careful balancing of aerodynamic and elastic properties to avoid aeroelastic instabilities. This is certainly a relevant topic of research. However, the approach of extracting general trends by analyzing the three IEA reference turbines (10 MW, 15 MW, and 22 MW) appears overambitious. These designs were developed at different times, by different teams (NREL and DTU), using tools of varying fidelity and maturity:
some discussion in https://iopscience.iop.org/article/10.1088/1742-6596/2767/5/052042/meta)
While the approach proposed by this manuscript might eventually become a valuable method for analyzing and proposing new designs, it does not currently provide a valid basis for drawing general conclusions about trends as blade length varies.
I hope the feedback is valuable and the author finds the time to incorporate feedback and resubmit. My recommendation would be to target a lower-bar publication, such as a conference proceeding. Events like TORQUE or AIAA SciTech would be suitable venues for publishing smaller studies.
Good luck and best regards