A Staged Approach to Erosion Analysis of Wind Turbine Blade Coatings
Round 1
Reviewer 1 Report
In the paper, the results are presented of a detailed experimental study for the erosion process of wind turbine blade coating under the impact of rain droplets. The significant advantage of the reported work is a variety of experimental tools to study different stages of erosion. The authors combine photographs, microscopy, x-ray computed tomography, and mass loss. Five stages of the erosion process are thoroughly investigated. The results obtained give insight into the mechanisms associated with material destruction. Of course, it would be desirable to have some generalization of the results, empirical formulas for mass loss estimation, recommendations for coating manufacturers. Nevertheless, the paper contains valuable information adequate to justify publication. Overall, the paper is well organized, and the material is given in a clear form. There are no specific critical comments from my side. Just minor corrections are desirable.
- The list of references should be widened. It is an actively developing area, and the results of other researchers should be discussed in the paper.
- The authors should check the correspondence of figure numbers in the text. There are no figures 11 and 12.
- Authors describe the initial stage of coating destruction in the following way “The air pockets from Stage 1 have collapsed due to the impacting rain droplets, the air pocket sites have now developed into pits. As the sample is exposed to further rain droplets, these pits begin to grow and merge…” The air pockets are somehow connected with the surface roughness. Thus characteristics of the surface could be specified to understand mean air pockets size. Perhaps the role of the surface treatment could be touched concerning the erosion rate.
Author Response
Additional references added as requested and figure numbers revised and updated as requested.
No other changes requested.
Reviewer 2 Report
My review
A Staged Approach to Erosion Analysis of Wind Turbine Blade Coatings
Wind turbine manufacturing technologies have undergone a significant transformation in recent years. The changes concerned mainly the reduction of the cost of obtaining generated energy by increasing the size and power of wind turbines, as well as reducing the costs of their operation and maintenance.
As the size of wind turbines increases, so does the speed at which the blade tip moves, which in turn accelerates leading edge erosion from rain, dust and airborne particles. The increase in erosion affects not only the damage itself, but also its frequency.
Current research on the erosion of leading wind turbines focuses, among others, on the end of the incubation period and a breakthrough in the analysis of the erosion mechanism.
In pursuit of the assumed goals of the work entitled A Staged Approach to Erosion Analysis of Wind Turbine Blade Coatings, the experimental Whirling Arm Erosion test stand was used (to study various damaging mechanisms) designed / built and characterized at the Energy Technology Center (ETC) in East Kilbride, Great Britain.
The peer-reviewed work A Staged Approach to Erosion Analysis of Wind Turbine Blade Coatings presents the benefits of splitting and describing the progression of leading edge erosion into distinct stages. The phased approach to rain erosion research provides a more in-depth look at the erosion process and allows, above all, to assess the initiation and development of erosion. Five steps are characteristic: (1) undamaged, like a new sample; (2) between the undamaged sample and the end of the incubation; (3) end of the incubation period; (4) between the end of incubation and the breakthrough and (5) the breakthrough.
The experimental results from the staged erosion method were characterized by photos, photographs, microscopic images, X-ray computed tomography (XCT) slices and measurements of weight loss.
Looking at all the presented data, it is clear that erosion is concentrated in a specific zone of the sample surface.
Looking at all the presented data, it is clear that erosion is concentrated in a specific zone of the sample surface. When analyzing the subject matter - the model of approach to the analysis of erosion of wind turbine blade coatings, the reviewer's attention is drawn to the fact that further research/continuation of works, and above all identified characteristic changes in the process development, should be used during industrial tests of coating systems.
This should provide greater detail in the "performance" of the coating, allowing greater certainty in predicting the life of the wind turbine blade shell. In the summary of the work, this aspect of the research and its importance for the economy should be clearly discussed. Moreover, I believe that the work should contain more thematic citations of literature (7 is definitely not enough). The literature on the subject should emphasize the importance of this research and its progress in the field of wind turbine manufacturing technologies.
To sum up, according to the reviewer, the work A Staged Approach to Erosion Analysis of Wind Turbine Blade Coatings after completing the literature review, editing /emphasizing the importance of the research and minor linguistic correction, is ready for publication.
Author Response
Minor comments addressed and relevant references added.
As reviewer notes - the field is constantly evolving, and as such, new work is emerging monthly. The authors have used only those references which have a direct bearing on the work presented.
Reviewer 3 Report
The manuscript entitled “A Staged Approach to Erosion Analysis of Wind Turbine Blade Coatings” authored by David Nash, Grant Leishman, Cameron Mackie, Kirsten Dyer and Liu Yang describes the evolution and analysis of leading-edge erosion on wind turbine blades. Authors of this paper presenting one of the important issues of wind turbine technology, such as erosion analysis which focus on material changes at each stage of the erosion process. The model-based analysis predicts how the coating mechanism of offshore wind blades changes, and ultimately fails, due to the impact of rain droplet.
Although the scientific content of the paper is adequate for publication, there are still problems with English language. Therefore, a thorough revision of the manuscript is required before publishing it.
There is a lack of references. Please add more references in the manuscript.
In the Tables, please include the “units” in the heading of a table instead of repeating it in every row and column.
In the Figures, “Axis Titles” must be clear (big font size) and identical in all figures.
The corrections recommended are:
Q1. Page2, Line-56 “The five stages chosen are shown in the adjacent figure. Stage 1”
Please correct adjacent figure as “Figure 1”
Q2. P2, L-58, “existing defects or voids below the surface and how these affect the materials ability to.
Please correct the materials as material’s
Q3. P2, L-60, “no damage visible on the surface of the sample but will be interesting to see if there are”.
Please correct the sentence as “will be interested”
Q4. P2, L-72, In figure 1, the axis title looks blurred. Please increase the font size. Also please elaborate the figure 1 caption little bit more so that the reader can understand the context.
Q5. P2, L-73, “Currently standard industry practice is too only look at Stages 1, 3 & 5, so by including”
Please correct the sentence.
Q6. P2, L-75-76, “the sample is still undamaged but, by examining this stage in detail, any material property changes, or sub surface variations can be detected”.
What material property (sub surface variations) can be changed? Please explain. How do you characterize it? Please give references that support your arguments.
Q7. P2, L-77-78, “changes in the filler can be detected thus giving insight into the mechanisms associated with break-through”.
What changes occurred in the filler and how do you explain the mechanisms associated with the break-through? Give reference to similar work conducted by others and explain what similarity/differences you found in this study.
Q8. P3, L-89, “ability to vary shroud height and run at up to 1400rpm.”.
Leave a space between 1400 and rpm in “1400rpm”.
Q9. P3, L-119, In Figure 2. Rain Erosion Test (RET) rig.
Please elaborate the figure caption.
Q10. P4, L-127, Table 1: Rotational speed to linear speed.
Elaborate the Table I caption. Please remove the RPM and m/s from Table I and add it in the “column heading” as Rotation Speed (RPM) and Linear Speed (m/s).
Q11. P4, L132-133, “This upgrade meant that the variation between the radii of needles is 2mm which results in a very precise impact location”.
Please correct the sentence and add a space between 2 and mm in “2mm”.
Q12. P4, L-135, Please add space between 1200 and rpm in “1200rpm”.
Q13. P4, L-138-139, “The time taken to reach each stage is consistent, apart from sample A007 which failed due to a different failure mechanism, reaching Stage 4 before any testing could be conducted.”
Please explain why sample A007 failed? What was the failure mechanism happened in A007 sample?
Q14. P4, L-146, “Each specimen has three distinct layers–substrate, filler and LEP.
Please define “LEP”?
Q15. P4, L-142-146, The authors mentioned that “The test specimens were manufactured using an arrangement of bi-axial and unidirectional glass fibre mat, set in an epoxy resin. The glass fiber reinforced polymer substrate was then coated with the wind turbine blade leading edge coating system, according to the manufacturers guidelines”.
“Please explain briefly how you made the samples. Give reference to “the manufacturers guidelines”.
Q16. P5, L-153, Please elaborate the heading “4.1. Photographs”.
Q17. P5, L-157, Please elaborate the heading “4.2. Microscopy”.
Q18. P8, L-173, Correct the Table 3 and Table 4 by adding a “space” between number and percentage sign (for example: 0.38 %).
Q19. P8, L-175, Elaborate the heading as: “4.4. Mass Loss of---------------”
Q20. P8, L-186, In Figure 6. The Title of the Graph is given as “Mass Loss vs Erosion stage and Mass Loss vs Impact Energy. However, the Y-axis Label of both graphs and the Figure caption are given as, Plots of “mass lost vs: Erosion stage” and “mass lost vs Impact Energy”
Please correct the Y-axis Label, Graph Title and Figure 6 caption “identical”.
Q21. P8, L-188-189, “Stage 3, show in Figure 3(c), displays the sample just at the incubation period has come to an”
Please correct show as “shown”.
Q22. P10, L-252, “Considering the mass measurements taken at each stage of erosion, Figure 11, is it clear that”
Please correct the sentence as “it is clear that”
Q23. P10, L-267-270, “Additional to the data presented in this paper, a Fourier transform infrared (FTIR) spectroscopy study was undertaken to look at any change in the chemical bond groups within the coating’s top surface, the LEP. This study found that as the erosion stages progressed during RET, no change in chemical bond groups was detected”.
Please add the results of FTIR study and add some references that support your arguments.
Q24. P10, L-292, “The staged approach model allows these changes to explored further thus providing a more complete picture”.
Please correct the grammar.
Q25. Authors mentioned that “the current investigation focused on two main areas: (1) the end of incubation period and (2) the total lifetime of the material”.
Based on your model how did you validate the incubation period and predict the total lifetime of the material. Please include a description in the conclusion.
Comments for author File: 
Comments.pdf
Author Response
All comments fully accepted and addressed.
Most are typographical and English corrected.
Q6. P2, L-75-76, “the sample is still undamaged but, by examining this stage in detail, any material property changes, or sub surface variations can be detected”.
What material property (sub surface variations) can be changed? Please explain. How do you
characterize it? Please give references that support your arguments.
Response - Issue of characterisation using void volume added and references added.
Q7. P2, L-77-78, “changes in the filler can be detected thus giving insight into the mechanisms associated with break-through”.
Response - text revised and void volume issue included.
Q13. P4, L-138-139, “The time taken to reach each stage is consistent, apart from sample A007 which failed due to a different failure mechanism, reaching Stage 4 before any testing could be conducted.”
Please explain why sample A007 failed? What was the failure mechanism happened in A007 sample?
Response - A007 is thought to have failed due to manufacturing issue or presence of pre-existing defect - text revised accordingly.
Q15. P4, L-142-146, The authors mentioned that “The test specimens were manufactured using
an arrangement of bi-axial and unidirectional glass fibre mat, set in an epoxy resin. The glass
fiber reinforced polymer substrate was then coated with the wind turbine blade leading edge
coating system, according to the manufacturers guidelines”.
“Please explain briefly how you made the samples. Give reference to “the manufacturers
guidelines
Response - new text included to outline manufacturing approach
Q23. P10, L-267-270, “Additional to the data presented in this paper, a Fourier transform infrared (FTIR) spectroscopy study was undertaken to look at any change in the chemical bond groups within the coating’s top surface, the LEP. This study found that as the erosion stages progressed during RET, no change in chemical bond groups was detected”.
Please add the results of FTIR study and add some references that support your arguments.
Response - FTIR results not added as the additional information does not enhance the arguments - references added.
The authors thank the reviewer for a highly detailed and helpful review
