Land-based wind turbines with flexible rail-transportable blades – Part 2: 3D finite element design  optimization of the rotor blades

Camarena, Ernesto; Anderson, Evan; Paquette, Josh; Bortolotti, Pietro; Feil, Roland; Johnson, Nick

doi:https://doi.org/10.5194/wes-7-19-2022

Articles | Volume 7, issue 1

https://doi.org/10.5194/wes-7-19-2022

© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/wes-7-19-2022

© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 7, issue 1

Research article

|

19 Jan 2022

Research article |

| 19 Jan 2022

Land-based wind turbines with flexible rail-transportable blades – Part 2: 3D finite element design optimization of the rotor blades

Ernesto Camarena, Evan Anderson, Josh Paquette, Pietro Bortolotti, Roland Feil, and Nick Johnson

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Final revised paper (published on 19 Jan 2022)
Preprint (discussion started on 27 Aug 2021)

Interactive discussion

Status: closed

CC1:
'Comment on wes-2021-74', Malo Rosemeier, 30 Aug 2021

This paper presents well one of the few optimization studies which constrains the blade's buckling resistance. A linear buckling analysis was conducted in ANSYS using SHELL181 type elements. The element size is unknown.
This comment should be considered as a suggestion for a realistic exploitation of the buckling reserves of a wind turbine blade design:

Fig. 10 shows a critical buckling mode on the suction side in the leading edge panel. This mode shape seems to have a very short wave length and a narrow width. Therefore this mode might be related to a local buckling failure mode like core shear crimping, cf. Fig. 4a and Fig. 6c in Rosemeier et al., 2018. Core shear crimping can become critical when the through-the-thickness shear stiffness is low compared to the bending stiffness of the face sheets. Sometimes this failure mode can be easily circumvent by a more realistic modeling, i.e., by taking the resin uptake of the core in the material parametrization into account. The resin uptake is a function of the core thickness, the slit width, the slitting pattern, and the microstructure of the core material.
Reference:

Rosemeier, Malo, P. Buriticá, and Alexandros Antoniou. "Impact of resin uptake of core materials on buckling of wind turbine blades." In Journal of Physics: Conference Series, vol. 1037, no. 4, p. 042001. IOP Publishing, 2018. https://doi.org/10.1088/1742-6596/1037/4/042001

Disclaimer: this community comment is written by an individual and does not necessarily reflect the opinion of their employer.

Citation: https://doi.org/10.5194/wes-2021-74-CC1
- AC2: 'Reply on CC1', Ernesto Camarena, 19 Nov 2021
  
  We thank you for your feedback. Note that Figure 10 shows Tsai-Wu failure indices. Assuming you mean Figure 11, then, yes, the wavelength is very short and could be investigated further for possible gains in buckling strength. Note, though that in Table 6, the BAR-DRG (BAR-DRG is in Figure 11) both the buckling and rupture constraint are active. Thus, any improvements to the buckling resistance would not necessarily increase the total blade strength since the rupture constraint value would likely be unchanged. But, yes it could increase the buckling reserves.
  
  Citation: https://doi.org/10.5194/wes-2021-74-AC2
RC1:
'Comment on wes-2021-74', Anonymous Referee #1, 30 Sep 2021
This is not the easiest paper to review because of the large amount of information contained. In my opinion, the paper is very well written, the analysis provided is highly valuable for the wind energy community and the contribution is original.

However, although I know the field, I am not expert in structural design of wind turbine blades. This is why, first I recommend the editor to incorporate to the review process experts in the field of blade structural design analysis and its optimization, who really will provide a more specific sound advice on the acceptance of the paper.

Considering my background, I think I can contribute with some general comments that could clarify some points of the study for the wind energy community.

The authors propose a detailed FEM analysis of different structural design options. It is not clear if their designs, that on the other hand lead to very flexible blades, can present deformation of the blade sections shapes that could affect the performance of the airfoils. A comment on this aspect could be convenient, because if this is the case, then a simple Blade Element Momentum approach (such as the one implemented OpenFast) will not be enough for determining the aerodynamic loads.

One general doubt is if there is any verification of the impact of the different blade designs on the power production of a wind turbine using the different blade options. Again a comment on this aspect could be convenient.

Commenting on how the different blades (different structural designs) will interact with the rest the wind turbine, or at least a comment clarifying that this aspect is relevant and will be treated in future research, would be convenient.

In general, some comments should be included on the necessity of checking the influence of the different proposed design options on the aeroelastic behaviour of whole wind turbine and in particular the interaction with the tower dynamics and the implications related to the control of the wind turbine.
Citation: https://doi.org/10.5194/wes-2021-74-RC1
RC2:
'Comment on wes-2021-74', Anonymous Referee #2, 13 Oct 2021
This paper is part of an interesting piece of research that investigates both on a system level and a detailed blade structural design level. The paper is well written and offers a lot of information, but there also some aspects that can be elaborated on.

Especially the implications of high flexibility necessary for rail transport in the USA will trigger the potential reader. In this paper however a ‘rail transport’ constraint is missing, which is a pity since it could illustrate the consequence of the lower design strain for the Heavy-Tow carbon compared to the uniaxial glass or the industry-standard carbon fiber.

The reader could now conclude from Part 1 of this study (see wes-2021-29) that for each material a maximum strain of 3500 µstrain has been allowed. That would be low for uniaxial glass but high for the Heavy-tow carbon fiber.

The blade design is discussed in Ch. 4.3 only briefly. It would help the reader to learn more about the choices made regarding the components. To name some questions that could be answered:

Has carbon fiber also been used for the LE and TE reinforcements?

The TE panel is a sandwich with triax facings, has that also been used for he LE panels?

Usually, the root section of a blade mainly consists of triax material, has that been used here too (Figures 14-16 do suggest something like that)?

Some notes on the ANSYS analysis. For the ANSYS model shell181 has been used. Shell elements like shell181 are suspected to give an incorrect estimate of the torsional stiffness and thereby of the shear stresses due to torsion (and maybe also shear forces). Would an inaccuracy of 30% in torsional (shear) stress lead to another ranking in blade designs?

The Tsai-Wu criterion is applied, but line 257 mentions ‘that neglects any effects due to transverse normal stress’. What is mentioned here: all transverse normal stresses, i.e. all non-spanwise normal stresses, or only the normal stress perpendicular to the laminate plane?

For the Heavy-Tow carbon fiber most probably material data are used for pultruded profiles. If that is the case the spar cap will have discrete thickness steps (the pultrusion thickness), which will lead to a somewhat higher blade mass. At the thickness step a stress peak will occur which lowers the strength locally which again leads to an increase in blade mass. What consequences would this have?
Citation: https://doi.org/10.5194/wes-2021-74-RC2
AC1: 'Comment on wes-2021-74', Ernesto Camarena, 19 Nov 2021

The authors would like to thank the associate editor Prof. Sandrine Aubrun and the two reviewers for their time and valuable feedback. We believe that these inputs have contributed to the improvement of the paper as well as increasing the author’s knowledge of the field in general. Below you will find a list of point-by-point replies to the reviewers’ comments. The text from the reviewers is reported in italics and has been divided into a numbered list. Each point is followed by the authors’ reply.

Citation: https://doi.org/10.5194/wes-2021-74-AC1

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

AR by Ernesto Camarena on behalf of the Authors (19 Nov 2021) Author's response Author's tracked changes Manuscript

ED: Publish as is (28 Nov 2021) by Sandrine Aubrun

ED: Publish as is (06 Dec 2021) by Jakob Mann (Chief editor)

AR by Ernesto Camarena on behalf of the Authors (10 Dec 2021)

Short summary

The length of rotor blades of land-based wind turbines is currently constrained by logistics. Turbine manufacturers currently propose segmented solutions to overcome these limits, but blade joints come with extra masses and costs. This work investigates an alternative solution, namely the design of ultra-flexible blades that can be transported on rail via controlled bending. The results show that this is a promising pathway to further increasing the size of land-based wind turbines.