CFD-Based In-Depth Investigation of the Effects of the Shape and Layout of a Vortex Generator on the Aerodynamic Performance of a Multi-MW Wind Turbine
Round 1
Reviewer 1 Report
In attached file.
Comments for author File: 
Comments.pdf
Author Response
A Review
The authors perform an in depth study on the effects of vortex generators on flow separation and lift coefficient. They make use of a RANS equations with SST turbulence model to analyze the combine turbine + vortex generator geometries. They also perform parametric study to identify the effects of chord wise length, height and spacing of the vortex generators. The analysis is sound in set up and accuracy, as can be seen by the verification study performed by the authors. There are however still issues that must be clarified. This reviewer does NOT recommend accepting the manuscript until the comments are addressed. Once the recommended suggestions are implemented, the manuscript will be much stronger and well received by the wind energy community.
Major Comments:
1) Table 2: what is ‘ea’
> Corrected to reflect the comments. Thank you for your comment.
2) Section 3.1: The author seek to validate their numerical model (RANS + SST) using data obtained using Blade Element Momentum Theory (BEMT). This however is not correct since the RANS model produces more accurate results than BEMT. The validation study should be performed by comparing the RANS models with a more accurate model (LES/DES) or experimental data. Therefore, this validation study is not appropriate and has no merit. Experimental validation was previously performed for various turbines; see for example Reddy, Dulikravich, Sobieczky, Gonzalez, “Bladelets – Winglets on Blades of Wind Turbines: A Multi objective Design Optimization Study,” Journal of Solar Energy Engineering.
> In this paper, we proceeded with research on the UNISON U113 blade in operation in South Korea. The turbine was designed using GH-bladed, a BEMT-based professional licensing program, which has been compared to production SCADA measurement data. It is difficult to open detailed information because it has an NDA with UNISON, an installation company, but I can say that the BEMT value in this study is an real value. Thank you for recommending a good study.
3) How were the RANS + SST equations solved? Did the authors use a commercial package such as Ansys Fluent?
> As mentioned in the introduction, RANS + SST k-w equations solved via Ansys CFX, a commercial CFD tool.
4) Figure 14 and Fig. 15. The authors should replace with axis in the figures ‘Parameter 1’, etc. with the name of the parameter. Also state what the parameters being studied are. This is nowhere to be seen in Section 3.4
> Corrected to reflect the comments. Thank you for your comment.
5) The authors state that a response surface method was used to perform the parametric study, but nowhere in the manuscript do they present the formulation of this RSM method. The authors should explicitly state the formulation of the method used.
> Thank you for your comment. I used LOWESS 2nd equation and I fixed it.
6) Conclusion, Point #2: The authors claim to have performed optimization of the turbine + vortex generator but this is nowhere to be seen. They simply perform parametric study by manually varying the values of the various parameters. True (numerical) optimization studies involves minimizing/maximum one or several cost function/objectives simultaneously using gradient based methods (BFGS, SQP) or evolutionary methods (genetic algorithm, particle swarm). Manually varying parameters in an RSM approximation is not considered optimization. The authors are encouraged to perform a proper optimization study or simply remove any mention of optimization in the manuscript.
> Thank you for your comments. RSM has been found to be commonly used as a classic optimization tool. Optimization experts haven't used it well, but it's easy to use and I can find it used by many researchers. The following is an optimization paper that utilizes RSM.
Huai-Zhi Han, “Multi-objective shape optimization of double pipe heat exchanger with inner corrugated tube using RSM method”, International Journal of Thermal Sciences, Volume 90, 2015, Pages 173-186, ISSN 1290-0729, https://doi.org/10.1016/j.ijthermalsci.2014.12.010.
Y. K. Choi, H. S. Yoon and C. S. Koh, "Pole-Shape Optimization of a Switched-Reluctance Motor for Torque Ripple Reduction," in IEEE Transactions on Magnetics, vol. 43, no. 4, pp. 1797-1800, April 2007, doi: 10.1109/TMAG.2006.892292.
M. Oudjene, L. Ben-Ayed, A. Delamézière, J.-L. Batoz, “Shape optimization of clinching tools using the response surface methodology with Moving Least-Square approximation”, Journal of Materials Processing Technology, Volume 209, Issue 1, 2009, Pages 289-296, ISSN 0924-0136, https://doi.org/10.1016/j.jmatprotec.2008.02.030.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The manuscript entitled “CFD-based in-depth investigation of the effects of the shape and layout of a vortex generator on the aerodynamic performance of a multi-MW wind turbine” deals with a very interesting and timely topic in wind energy literature, which is the analysis of the effect of vortex generators on wind turbine blades.
The manuscript is in general well written (apart from minor typos which I suggest to check) and well organized. The application of the methods and the results are consistent.
My major concern regards the novelty of this study. In my opinion, the authors have not analyzed the vast literature on the topic and therefore the manuscript lacks focus in the definition of the objectives and the explanation of the novelty.
I suggest here on some references which the authors are encouraged to read and include in the literature review. Basing on these, as well as whatever other the authors might want to include, in my opinion it could be possible to elaborate better on the novelty of the paper and to state it clearly.
- Aramendia, I., Fernandez-Gamiz, U., Ramos-Hernanz, J. A., Sancho, J., Lopez-Guede, J. M., & Zulueta, E. (2017). Flow control devices for wind turbines. In Energy Harvesting and Energy Efficiency(pp. 629-655). Springer, Cham.
- Chillon, S., Uriarte-Uriarte, A., Aramendia, I., Martínez-Filgueira, P., Fernandez-Gamiz, U., & Ibarra-Udaeta, I. (2020). jBAY modeling of vane-type vortex generators and study on airfoil aerodynamic performance. Energies, 13(10), 2423.
- Fernandez-Gamiz, U., Zulueta, E., Boyano, A., Ansoategui, I., & Uriarte, I. (2017). Five megawatt wind turbine power output improvements by passive flow control devices. Energies, 10(6), 742.
- Li, X. K., Liu, W., Zhang, T. J., Wang, P. M., & Wang, X. D. (2019). Analysis of the effect of vortex generator spacing on boundary layer flow separation control. Applied Sciences, 9(24), 5495.
- Wu, Z., Chen, T., Wang, H., Shi, H., & Li, M. (2021). Investigate aerodynamic performance of wind turbine blades with vortex generators at the transition area. Wind Engineering, 0309524X211038542
I have a further observation in relation to the results and to the final comment in the conclusions section. There are few studies in the literature dealing with the real-world analysis (based on SCADA data) of the effect of vortex generators on wind turbine performance and, basing on those studies, in my opinion it is interesting to report the performance enhancement at different wind speeds because of course this quantity depends on the wind speed and therefore the actual impact on the Annual Energy Production of a wind turbine depends on the observed distribution on site. The studies are listed here below and I suggest to include them in the references. In particular, in the former, a 2.3 MW wind turbine is studied (like the one considered in the present study, I guess) and the test case study is very interesting because at first the VG have been installed on the wind turbine and the optimization is therefore purely aerodynamic. Few months later, the control of the rotational speed has been optimized too, in order to reach the optimum induction level while maintaining adequate angles of attack along the blade: this provides a further slight improvement of the wind turbine performance. Therefore, this study in my opinion could be inspiring for the purposes of the present paper.
- Astolfi, D., Castellani, F., Fravolini, M. L., Cascianelli, S., & Terzi, L. (2019). Precision computation of wind turbine power upgrades: An aerodynamic and control optimization test case. Journal of Energy Resources Technology, 141(5).
- Hwangbo, H., Ding, Y., Eisele, O., Weinzierl, G., Lang, U., & Pechlivanoglou, G. (2017). Quantifying the effect of vortex generator installation on wind power production: An academia-industry case study. Renewable Energy, 113, 1589-1597.
Author Response
Review #2
The manuscript entitled “CFD-based in-depth investigation of the effects of the shape and layout of a vortex generator on the aerodynamic performance of a multi-MW wind turbine” deals with a very interesting and timely topic in wind energy literature, which is the analysis of the effect of vortex generators on wind turbine blades.
The manuscript is in general well written (apart from minor typos which I suggest to check) and well organized. The application of the methods and the results are consistent.
My major concern regards the novelty of this study. In my opinion, the authors have not analyzed the vast literature on the topic and therefore the manuscript lacks focus in the definition of the objectives and the explanation of the novelty.
I suggest here on some references which the authors are encouraged to read and include in the literature review. Basing on these, as well as whatever other the authors might want to include, in my opinion it could be possible to elaborate better on the novelty of the paper and to state it clearly.
Aramendia, I., Fernandez-Gamiz, U., Ramos-Hernanz, J. A., Sancho, J., Lopez-Guede, J. M., & Zulueta, E. (2017). Flow control devices for wind turbines. In Energy Harvesting and Energy Efficiency(pp. 629-655). Springer, Cham.
Chillon, S., Uriarte-Uriarte, A., Aramendia, I., Martínez-Filgueira, P., Fernandez-Gamiz, U., & Ibarra-Udaeta, I. (2020). jBAY modeling of vane-type vortex generators and study on airfoil aerodynamic performance. Energies, 13(10), 2423.
Fernandez-Gamiz, U., Zulueta, E., Boyano, A., Ansoategui, I., & Uriarte, I. (2017). Five megawatt wind turbine power output improvements by passive flow control devices. Energies, 10(6), 742.
Li, X. K., Liu, W., Zhang, T. J., Wang, P. M., & Wang, X. D. (2019). Analysis of the effect of vortex generator spacing on boundary layer flow separation control. Applied Sciences, 9(24), 5495.
Wu, Z., Chen, T., Wang, H., Shi, H., & Li, M. (2021). Investigate aerodynamic performance of wind turbine blades with vortex generators at the transition area. Wind Engineering, 0309524X211038542
I have a further observation in relation to the results and to the final comment in the conclusions section. There are few studies in the literature dealing with the real-world analysis (based on SCADA data) of the effect of vortex generators on wind turbine performance and, basing on those studies, in my opinion it is interesting to report the performance enhancement at different wind speeds because of course this quantity depends on the wind speed and therefore the actual impact on the Annual Energy Production of a wind turbine depends on the observed distribution on site. The studies are listed here below and I suggest to include them in the references. In particular, in the former, a 2.3 MW wind turbine is studied (like the one considered in the present study, I guess) and the test case study is very interesting because at first the VG have been installed on the wind turbine and the optimization is therefore purely aerodynamic. Few months later, the control of the rotational speed has been optimized too, in order to reach the optimum induction level while maintaining adequate angles of attack along the blade: this provides a further slight improvement of the wind turbine performance. Therefore, this study in my opinion could be inspiring for the purposes of the present paper.
Astolfi, D., Castellani, F., Fravolini, M. L., Cascianelli, S., & Terzi, L. (2019). Precision computation of wind turbine power upgrades: An aerodynamic and control optimization test case. Journal of Energy Resources Technology, 141(5).
Hwangbo, H., Ding, Y., Eisele, O., Weinzierl, G., Lang, U., & Pechlivanoglou, G. (2017). Quantifying the effect of vortex generator installation on wind power production: An academia-industry case study. Renewable Energy, 113, 1589-1597.
> Thank you for your kind comment. I have read all the high-quality papers you recommended. Studies done by other researchers have helped me organize my thoughts and have given me an opportunity to think more about the objectives of my study. The academia-industry study of Texas A&M with Smart Blade was really helpful for me. The papers you recommended are referenced in the introduction and main text.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The authors have NOT satisfactorily addressed my comments:
1) For point number 5: "Thank you for your comment. I used LOWESS 2nd equation and I fixed it." Please provide a reference for this LOWESS method
2) I do not agree with the authors comments on Comment #6. The entire optimization community known that RSM is not an optimization algorithm; it is only a way to compute the performance of the design (function response). To perform optimization, the RSM still needs to be coupled with search algorithm (genetic, particle swarm, SQP). The author presents three studies where RSM was used to perform optimization but simply reading the abstract of these papers you will see that:
a) Huai-Zhi Han used Sequential Approximation Optimization (SAO) algorithm
b) Y. K. Choi used a genetic algorithm
c) M. Oudjene used Sequential Quadratic Programming
I will reiterate my comment from previous review " The authors are encouraged to perform a proper optimization study or simply remove any mention of optimization in the manuscript."
Author Response
Answers
Point 1) I Added explanation and reference to LOWESS 2nd equations. (Cleveland WS: Robust locally weighted regression and smoothing scatterplots. Journal of the American Statistical Association 1979, 74:829-836.)
Point 2) Thank you for the critical review. I followed your comments and removed everything about optimization from the manuscript. The study of VG shape optimization will be carried out again with an appropriate selection of genetic algorithms in the future. Thanks for kindly letting me know.
Reviewer 2 Report
The authors have addressed my comments. The paper can be published for me.
Round 3
Reviewer 1 Report
The authors are addressed all of my comments. The manuscript can now be accepted for publication.
