A Modeling Study Focused on Improving the Aerodynamic Performance of a Small Horizontal Axis Wind Turbine
Round 1
Reviewer 1 Report
The author has done a good job. A few comments are shown to improve the manuscript.
1. Novel aspects of the work must be highlighted.
2. Highlights of the work must be given in bullet format.
3. Formatting issues must be seriously resolved at priority.
4. Figure 12 needs readjustments and quality of the figures must be enhanced.
5. Table 2 must be shown close to the place where its first cited.
6. Abstract and conclusion must be supported with numerical values.
7. How you have found the parameters of chord width distribution and angle of twist distribution on numerical basis?
8. What are the impacts of seasonal variations on working of turbine across a year?
Author Response
Answers to the Reviewers’ Comments
Manuscript: sustainability-2187222
The following represent point-by-point answers to the reviewers’ comments. Appropriate revisions are made in the revised manuscript, as explained hereunder. In the revised version of the manuscript, all the revisions are highlighted in yellow.
Reviewer # 01 Comments:
- Novel aspects of the work must be highlighted.
Answer: The author is thankful to the reviewer for the valuable comment. As suggested, in the revised version of the manuscript, the novelty of the current work is discussed in the last paragraph of the introduction section, on page 3 of the revised manuscript.
- Highlights of the work must be given in bullet format.
Answer: The author is thankful to the reviewer for the valuable comment. As suggested, in the revised version of the manuscript, the highlights of the work are provided in bullet format on pages 1 & 2 of the revised manuscript.
- Formatting issues must be seriously resolved at priority.
Answer: The author is thankful to the reviewer for the valuable comment. As suggested, in the revised version of the manuscript, all the formatting issues have been resolved. The corrections are highlighted throughout the manuscript.
- Figure 12 needs readjustments and quality of the figures must be enhanced.
Answer: The author is thankful to the reviewer for the valuable comment. As suggested, in the revised version of the manuscript, Figure 12 has been readjusted and the quality of the figures has been enhanced.
- Table 2 must be shown close to the place where its first cited.
Answer: The author is thankful to the reviewer for the valuable comment. As suggested, in the revised version of the manuscript, Table 2 is shown close to the place where it is first cited.
- Abstract and conclusion must be supported with numerical values.
Answer: The author is thankful to the reviewer for the valuable comment. As suggested, in the revised version of the manuscript, the abstract and conclusion are supported with numerical values.
- How you have found the parameters of chord width distribution and angle of twist distribution on numerical basis?
Answer: The author is thankful to the reviewer for the valuable comment. As suggested, in the revised version of the manuscript, the details of finding the parameters of chord width distribution and angle of twist distribution is given in section 3 “Methodology”, on pages 6 & 7 of the revised manuscript.
- What are the impacts of seasonal variations on working of turbine across a year?
Answer: The author is thankful to the reviewer for the valuable comment. As suggested, in the revised version of the manuscript, the impacts of seasonal variations on working of turbine across a year is discussed on page 9 of the revised manuscript.
Finally, the author wish to thank the reviewer for his constructive remarks, which are well-taken and implemented to improve the clarity and quality of the manuscript. I thank you for the time you put in reviewing my paper and look forward to meet your expectations.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The paper presents an interesting study concerning the provision of starting characteristics for a small scale horizontal axis wind turbine. The topic is worthy of investigation and therefore your study is useful to the engineering community. However the author should address a number of faults regarding the present format of the article as well as please clarify some doubts about the approaches employed.
Line 18 - correct, the staring behavior
Line 47 - In 2020, the China remains … In English one writes the USA but, never, the China or indeed the Germany.
The paper could benefit from being proofread by a native English speaker.
Line 58 - … (Re) < 103), … Presumably you mean (Re < 10E3), … Please correct throughout.
The introduction chapter comprises a literature review section that mentioned a number of important horizontal axis turbine references but the bulk of the discussion, surprisingly, focused on vertical axis machines which, though interesting in their own right, have different starting characteristics and therefore should not in my opinion correspond to the most relevant section of this review.
Throughout - Various spelling of PRO E, PRO/E, Pro-e, Pro/e, …
Line 121 - … the axial force and torque are “find out” by considering momentum …
Line 164 - … tip speed “ration” …
Methodology - Your reference [30] Wright and Wood explained that the starting sequence required the implementation of a variation on the classic BEM formulation. They wrote “Conventional blade element momentum analysis was modified to assume no flow deceleration through the blades, and the net torque on the rotor equated to the product of rotational moment of inertia and angular acceleration. In other words, the aerodynamic torque is assumed to accelerate the blades, rather than extract kinetic energy from the wind”.
Was this approach followed in the current paper?
They also mentioned that … “ the uncertainty in characterising lift and drag characteristics of aerofoils at high a and low Re, with little data available at appropriate Reynolds numbers”.
What was the approach that was followed by the author with regards to the source of the coefficients of lift and drag for the various values of Reynolds numbers experienced by the blades during the acceleration to nominal conditions?
The impacts of resistive torques are critical for wind turbines during start phases in low wind speeds. This is because the aerodynamic torque produced by the blades may have the same magnitude of resistive torques of the system. Therefore the proper characterization of the resistive torques is crucial on the analysis of the starting performance of wind turbines. Resistive torques are due to bearing friction, generator static and dynamic torque and the inertia of the rotor together with the drag of the blades. Some of the items are calculated in ADAMS but the software required inputs. Would the author please clarify what these were please.
Line 259 - … the value of the torque is very less … Grammar. Suggest, very low.
Line 260 - … overcome the static fraction of the wind turbine?
Figure 11 - The starting time(s) is surprisingly small when compared with the plots of Figure 9 of your reference number 30 which corresponds to wind conditions similar to Cherat’s. There you see very lengthy idling times of the order of 30s with the entire starting process taking up to a full minute. Would the author please comment on this observation.
Conclusion - The author mentioned the idling time twice in the conclusion section of the article. However not once was the concept of the idling of the turbine addressed explicitly in the body of the paper beforehand. You do observe an idling phase in reference 30, Figure 9, but it is not really evident, to my mind, in your results as you always show a sustained acceleration. That phase is characterised by an incipient acceleration, indeed that is the broad concept of idling. This should be resolved as part of the corrections.
References - For example [1] Rehman, S. et al. (2018). Al authors should be explicitly named in the References. “et al.” is an abbreviation only suitable for the text of articles.
Author Response
Answers to the Reviewers’ Comments
Manuscript: sustainability-2187222
The following represent point-by-point answers to the reviewers’ comments. Appropriate revisions are made in the revised manuscript, as explained hereunder. In the revised version of the manuscript, all the revisions are highlighted in green.
Reviewer # 02 Comments:
- Line 18 - correct, the staring behavior.
Answer: The author is thankful to the reviewer for the valuable comment. As suggested, in the revised version of the manuscript, the correction has been made.
- Line 47 - In 2020, the China remains … In English one writes the USA but, never, the China or indeed the Germany.
Answer: The author is thankful to the reviewer for the valuable comment. As suggested, in the revised version of the manuscript, the correction has been made.
- The paper could benefit from being proofread by a native English speaker.
Answer: The author is thankful to the reviewer for the valuable comment. As suggested, in the revised version of the manuscript, the revised paper has been proofread by a native English speaker. The corrections are highlighted throughout the manuscript.
- Line 58 - … (Re) < 103), … Presumably you mean (Re < 10E3), … Please correct throughout.
Answer: The author is thankful to the reviewer for the valuable comment. As suggested, in the revised version of the manuscript, the correction has been made.
- The introduction chapter comprises a literature review section that mentioned a number of important horizontal axis turbine references but the bulk of the discussion, surprisingly, focused on vertical axis machines which, though interesting in their own right, have different starting characteristics and therefore should not in my opinion correspond to the most relevant section of this review.
Answer: The author is thankful to the reviewer for the valuable comment. As suggested, in the revised version of the manuscript, the introduction section has been revised.
- Throughout - Various spelling of PRO E, PRO/E, Pro-e, Pro/e, …
Answer: The author is thankful to the reviewer for the valuable comment. As suggested, in the revised version of the manuscript, the discrepancy has been resolved.
- Line 121 - … the axial force and torque are “find out” by considering momentum …
Answer: The author is thankful to the reviewer for the valuable comment. As suggested, in the revised version of the manuscript, the correction has been made.
- Line 164 - … tip speed “ration” …
Answer: The author is thankful to the reviewer for the valuable comment. As suggested, in the revised version of the manuscript, the correction has been made.
- Methodology - Your reference [30] Wright and Wood explained that the starting sequence required the implementation of a variation on the classic BEM formulation. They wrote “Conventional blade element momentum analysis was modified to assume no flow deceleration through the blades, and the net torque on the rotor equated to the product of rotational moment of inertia and angular acceleration. In other words, the aerodynamic torque is assumed to accelerate the blades, rather than extract kinetic energy from the wind”.
Was this approach followed in the current paper?
They also mentioned that … “ the uncertainty in characterising lift and drag characteristics of aerofoils at high a and low Re, with little data available at appropriate Reynolds numbers”.
What was the approach that was followed by the author with regards to the source of the coefficients of lift and drag for the various values of Reynolds numbers experienced by the blades during the acceleration to nominal conditions?
The impacts of resistive torques are critical for wind turbines during start phases in low wind speeds. This is because the aerodynamic torque produced by the blades may have the same magnitude of resistive torques of the system. Therefore the proper characterization of the resistive torques is crucial on the analysis of the starting performance of wind turbines. Resistive torques are due to bearing friction, generator static and dynamic torque and the inertia of the rotor together with the drag of the blades. Some of the items are calculated in ADAMS but the software required inputs. Would the author please clarify what these were please.
Answer: The author is thankful to the reviewer for the valuable comments.
The conventional BEM theory was used to calculate the initial wind turbine blade parameters. Different blade profiles were developed from the initial wind turbine blade profile by varying the chord lengths and blade angles.
Based on the BEM theory, a MATLAB function named “BEM function” was developed that takes number of blades, tip speed ratio, coefficient of lift, stations radii, and angle of attack as inputs. These initial input values were selected based on the similar studies performed in the literature for designing the wind turbine designs for low to medium wind speeds locations [23-25]. The BEM function gives blade parameters for the selected area in the northern areas of Pakistan.
Resistive torques due to bearing friction, generator static and dynamic torque and the inertia of the rotor together with the drag of the blades were considered in this study. The bearing is considered as a revolute joint and various inputs were provided at the joint such as static friction coefficient,
dynamic friction coefficient, stiction transition velocity, and transition velocity coefficient in order to take into account the resistive torques.
- Line 259 - … the value of the torque is very less … Grammar. Suggest, very low.
Answer: The author is thankful to the reviewer for the valuable comment. As suggested, in the revised version of the manuscript, the correction has been made.
- Line 260 - … overcome the static fraction of the wind turbine?
Answer: The author is thankful to the reviewer for the valuable comment. As suggested, in the revised version of the manuscript, the correction has been made.
- Figure 11 - The starting time(s) is surprisingly small when compared with the plots of Figure 9 of your reference number 30 which corresponds to wind conditions similar to Cherat’s. There you see very lengthy idling times of the order of 30s with the entire starting process taking up to a full minute. Would the author please comment on this observation.
Answer: The author is thankful to the reviewer for the valuable comment. The difference in the idling time could be due to the difference in the sizes of the wind turbine blades and also due to the fact that the blade parameters in reference 30 are not optimized and in the current study, the optimization process has been performed. A constant wind speed is considered in current study.
- Conclusion - The author mentioned the idling time twice in the conclusion section of the article. However not once was the concept of the idling of the turbine addressed explicitly in the body of the paper beforehand. You do observe an idling phase in reference 30, Figure 9, but it is not really evident, to my mind, in your results as you always show a sustained acceleration. That phase is characterised by an incipient acceleration, indeed that is the broad concept of idling. This should be resolved as part of the corrections.
Answer: The author is thankful to the reviewer for the valuable comment. As suggested, in the revised version of the manuscript, the correction has been made.
- References - For example [1] Rehman, S. et al. (2018). Al authors should be explicitly named in the References. “et al.” is an abbreviation only suitable for the text of articles.
Answer: The author is thankful to the reviewer for the valuable comment. As suggested, in the revised version of the manuscript, all the references have been revised.
Finally, the author wish to thank the reviewer for his constructive remarks, which are well-taken and implemented to improve the clarity and quality of the manuscript. I thank you for the time you put in reviewing my paper and look forward to meet your expectations.
Author Response File: Author Response.pdf
Reviewer 3 Report
1. 1. Abstract can be improved; clearer statements must be made. To overcome the low wind speed issue, lower or higher starting torque is required? Why did the optimized wind turbine show an increased starting torque? Is this correct?
2. 2. Citation of each reference should be correctly cited in what they do, not citing the general facts such as ref [18-19] are cited in general facts but not what they do. Check all citations.
3. 3 “The Blade Element Momentum (BEM) theory is used to calculate the optimized wind turbine blade parameters (blade angles and chord lengths) that correspond to maximum starting torque” In this context, in design of blade, do we need the “maximum torque” or we need to know the minimum torque required to overcome the inertia and friction?
4. 4 Format all equations in uniform format and using “equation tap” in word. All terms must be defined.
5. 5 Coefficient of Performance (COP) or Cp, it must be correctly used.
6. 6 In eq 19, what is the h?
7. 7 Some figures are not necessary and can be removed.
8. 8 Fig 10, caption can be edited by deleting the a, b, and c. Labels in the graph is enough.
9. 9 Quality of Fig 12 must be improved.
110. Table 2 should be rotated for ease of seeing.
111. Based on fig 12 and the objectives of this work, blade design is a main point for low wind speed location, so that results should reflect this issue. How can we design the blade for low wind speed use? conclusion must be revised.
Author Response
Answers to the Reviewers’ Comments
Manuscript: sustainability-2187222
The following represent point-by-point answers to the reviewers’ comments. Appropriate revisions are made in the revised manuscript, as explained hereunder. In the revised version of the manuscript, all the revisions are highlighted in Turquoise color.
Reviewer # 03 Comments:
- Abstract can be improved; clearer statements must be made. To overcome the low wind speed issue, lower or higher starting torque is required? Why did the optimized wind turbine show an increased starting torque? Is this correct?
Answer: The author is thankful to the reviewer for the valuable comments. As suggested, in the revised version of the manuscript, the abstract is now supported with numerical values and clearer statements have been added. Yes, it is correct. The starting torque should increase after optimization process. The starting torque is produced at the wind turbine blades due to its interaction with the incoming wind. The starting torque of the wind turbine should exceed the resistive torques due to bearing friction, generator static and dynamic torque and the inertia of the rotor, in order to start the wind turbine.
- Citation of each reference should be correctly cited in what they do, not citing the general facts such as ref [18-19] are cited in general facts but not what they do. Check all citations.
Answer: The author is thankful to the reviewer for the valuable comment. As suggested, in the revised version of the manuscript, citations of all references are now correctly cited.
- The Blade Element Momentum (BEM) theory is used to calculate the optimized wind turbine blade parameters (blade angles and chord lengths) that correspond to maximum starting torque” In this context, in design of blade, do we need the “maximum torque” or we need to know the minimum torque required to overcome the inertia and friction?
Answer: The author is thankful to the reviewer for the valuable comment. The starting torque should increase after optimization process that is performed based on the BEM theory. The starting torque is produced at the wind turbine blades due to its interaction with the incoming wind. The starting torque of the wind turbine should exceed the resistive torques due to bearing friction, generator static and dynamic torque and the inertia of the rotor, in order to start the wind turbine.
- Format all equations in uniform format and using “equation tap” in word. All terms must be defined.
Answer: The author is thankful to the reviewer for the valuable comment. As suggested, in the revised version of the manuscript, all the equations are now uniformly formatted using the equation tab in word. All the terms in the equations are also defined in the revised version of the manuscript.
- Coefficient of Performance (COP) or Cp, it must be correctly used.
Answer: The author is thankful to the reviewer for the valuable comment. As suggested, in the revised version of the manuscript, the term Cp is changed to COP in order to have uniformity throughout the manuscript.
- In eq 19, what is the h?
Answer: The author is thankful to the reviewer for the valuable comment. In equation 19, the term is η and it is the expected electrical and mechanical efficiencies.
- Some figures are not necessary and can be removed.
Answer: The author is thankful to the reviewer for the valuable comment. As suggested, in the revised version of the manuscript, Figures 6 and 7 has been removed.
- Fig 10, caption can be edited by deleting the a, b, and c. Labels in the graph is enough.
Answer: The author is thankful to the reviewer for the valuable comment. As suggested, in the revised version of the manuscript, the caption of Figure 10 (Figure 8 in the revised version of manuscript) has been edited.
- Quality of Fig 12 must be improved.
Answer: The author is thankful to the reviewer for the valuable comment. As suggested, in the revised version of the manuscript, the quality of Figure 12 (Figure 10 in the revised version of manuscript) has been improved.
- Table 2 should be rotated for ease of seeing.
Answer: The author is thankful to the reviewer for the valuable comment. As suggested, in the revised version of the manuscript, Table 2 has been rotated for the ease of seeing.
- Based on fig 12 and the objectives of this work, blade design is a main point for low wind speed location, so that results should reflect this issue. How can we design the blade for low wind speed use? Conclusion must be revised.
Answer: The author is thankful to the reviewer for the valuable comment. As suggested, in the revised version of the manuscript, conclusion has been revised. Conclusion is now supported with numerical values and clearer statements have been added.
Finally, the author wish to thank the reviewer for his constructive remarks, which are well-taken and implemented to improve the clarity and quality of the manuscript. I thank you for the time you put in reviewing my paper and look forward to meet your expectations.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
All comments are addressed.
Author Response
Answers to the Reviewers’ Comments
Manuscript: sustainability-2187222
Reviewer # 01 Comments:
- All comments are addressed.
Answer: The author is thankful to the reviewer for the valuable comments, which were well-taken and implemented in the revised manuscript and has improved the clarity and quality of the manuscript.
Author Response File: Author Response.pdf
Reviewer 3 Report
The paper has been greatly improved as per suggested. However, for the COP which is stated to improve from 4.2 to 4.9, based on fig 10, I cannot agree with the number. The COP should not more than 1. If it is a mistake, edit all places mentioned about.
Author Response
Answers to the Reviewers’ Comments
Manuscript: sustainability-2187222
The following represent point-by-point answers to the reviewers’ comments. Appropriate revisions are made in the revised manuscript, as explained hereunder. In the revised version of the manuscript, all the revisions are highlighted in Yellow color.
Reviewer # 03 Comments:
- The paper has been greatly improved as per suggested. However, for the COP which is stated to improve from 4.2 to 4.9, based on fig 10, I cannot agree with the number. The COP should not more than 1. If it is a mistake, edit all places mentioned about.
Answer: The author is thankful to the reviewer for the valuable comments, which were well-taken and implemented in the revised manuscript and has improved the clarity and quality of the manuscript. As suggested, in the revised version of the manuscript, the values of the COP have been corrected in the abstract on page 1 and in the conclusions section on page 15 of the revised manuscript and are highlighted in yellow.
Author Response File: Author Response.pdf
