Investigating and Analyzing the Potential for Regenerating Excess Energy in a Helicopter UAV
Round 1
Reviewer 1 Report
This paper investigates the problems related to energy recovery of unmanned helicopters in the aerospace field, and verifies the existence of excess power under specific operating conditions through CFD simulations and wind tunnel experiments. There are some problems, which must be solved before it is considered for publication.
1. In page 1, ABSTRACT, authors are suggested to start broad in the general background, then narrow in on the relevant topic that will be pursued in the paper. Maybe this part can be improved.
2. Relevant research background needs to be supplemented in INTRODUCTION. And you should cite all papers you use properly.
3. Another obvious problem with this paper is lack of sufficient explanation of the simulation results. You need to explain your simulation results in detail and why you got such results.
4. Figure 1, Figure 8 and Figure 9 in your paper are a bit blurry. Please consider replacing them with clearer.
5. The experimental data points for the corresponding conditions are missing in Figures 11 and 12, please consider completing them to make the data more complete.
6.The experiment video should be listed in suport files.
Major revision
Author Response
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Author Response File: 
Author Response.docx
Reviewer 2 Report
The authors presented a Numerical and experimental study on the Potential of Regenerating Excess Energy in Helicopter UAV.
The authors investigated the possibility of recovering excess power from the helicopter UAV which constitutes the energy surplus from the helicopter's safety measures and its aerodynamic behavior during forward flight. They performed computational and experimental studies, to evaluate the helicopter UAV's performances under various operating conditions.
The paper is generally well prepared and can be accepted for publication after addressing the following points:
The novelty of the paper is to be clearly stated.
What is the convergence criterion?
A grid sensitivity test is to be performed.
How is the mesh treated close to the rotating domains? Have you used a moving mesh?
What is the convergence criterion?
What is the time step?
The used turbulence model is to be justified.
The boundary conditions are to be expressed mathematically.
What are the dimensions of the computational domain? To be justified.
What is the considered range for Reynold number?
Information about the characteristics of the used computer and computational time are to be mentioned.
For the experimental study, more details on the measurement techniques and data acquisition system are to be provided.
An experimental uncertainty study is to be performed.
The scientific soundness is to be improved by adding physical interpretations.
English level is relatively low and should be improved.
English level is relatively low and should be improved.
Author Response
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Author Response File: Author Response.docx
Reviewer 3 Report
The presentation, in general, is good, but it could be better to separate the images and explain them in a separate form, for example, Figures 1 and 6. I suggest a maximum of two graphics or images per Figure.
1) This work analyzes the excess power from a scale helicopter (UAV) in two flight conditions: hover and forward. The results are presented in simulations and experiments in a wind tunnel. The main contribution is the fluid analysis to know
the efforts of the helicopter UAV, and this analysis can be used for research thinking in future applications and understanding the conditions of flight where it can be used. And the experimental results are the principal strengths of this work.
2) In general, the work is good, but I think it would be more complete if the test in simulations and experiments included other movements or rotations like roll and yaw, and analyzing the excess power of the helicopter Unmanned Aerial Vehicle
(UAV). Also, adding an aerodynamic model of the Unmanned Aerial Vehicle (UAV) and reporting the response of the Euler angles and angular rates when the helicopter UAV is subject to such excess power is also good (I know it will take a lot of time for the authors, but future work may be acceptable).
3) Finally, my last suggestions are:
1.- Figure 6 contains four graphics, which should be separate and explain every graphic.
2.- Mention the software used for the analysis.
3. Mention the communication protocol between the UAV and the computer to obtain the data.
4.- Mention if, for the experiment, disable the roll and yaw angles and why.
5.- Analyzing the yaw and roll angles will be interesting (subject to the same conditions).
My best regards.
Author Response
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Author Response File: Author Response.docx
Reviewer 4 Report
This article investigated the behavior of excess power from a helicopter UAV and got some results. But the content of this paper is a little bit strange. I think it should be improved for acceptance.
At first, the author said that the CFD method and the experimental test were employed to investigate the excess power behavior of a helicopter UAV. However, the simulation with helicopter rotor for aerodynamics is quite normal. They just described the lift and the shape of the rotor blade is quite normal, only rectangular. Findings about what the simulation results describe can be found in any books on helicopter aerodynamics. I did not see any connection between the numerical simulation results and excess power behavior. From my perspective, it is enough to use experiments to study the research.
For details, there are some places that could be improved.
1. In CFD simulation, the details of computational grid information should be listed, such as the number of grids for each component grid, and the number of prism layers used for modeling the boundary flow, and so on so forth.
2. More details of the numerical method should be mentioned in this study, such as the numerical schemes for convective and viscous terms.
3. A grid independence analysis should be carried out to check the correctness of your employed computational grids.
4. Since you are using the incompressible URANS equations, please modify the mass equation (equation 1) to the incompressible form.
5. On Page 4, line 150. please give the value of parameters beta, sigma, and gamma.
6. On Page 4, line 151. What is the convergence criterion? Please give more information.
7. I don't understand why the author uses two figures (Figure 6 (a), (b)) to describe the same things. Because in these two figures, no new results are presented here. Only one plot would be appreciated. Similar things can be found in Figures 6(c), (d), 7, 10, 11, and 12.
8. I am confused by the value of 2.99%. Why is 2.99% in the third point of the conclusion section?
As for me, the language of this paper is OK, but it should be improved for fluency and readability.
Author Response
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Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
Accept in present form
Author Response
Thank you for accepting our manuscript. Our paper has improved substantially with all of your valuable comments.
Reviewer 4 Report
In the response letter, some of my concerns are addressed, but I am not satisfied with the quality of this paper yet. Some places in this manuscript still need to be improved.
1. As the abbreviation for Computational Fluid Dynamics is indicated at the beginning of the content (line 107), there is no need to display a full name similar to Computational Fluid Dynamics (CFD) in subsequent paragraphs. Just using CFD instead of using Computational Fluid Dynamics (CFD).
2. In line 130, the author said that a structured grid system was employed in this study, but the following plot showed the unstructured grid. It is so weird. Please clarify which kind of mesh are you using in the numerical investigation. In addition, I want to let you know that the citation here is inappropriate.
3. In lines 137, 141, 142, 170, and 197, using the word 'propeller' instead of 'rotor' to describe the main rotor of a helicopter is not professional.
4. In line 164, please explain the Reynolds number of simulations. What is the reference length of the Reynolds number? Airfoil chord or rotor radius?
5. In lines 166-167, the last sentence seems to relate to the grid information, but there is not any grid appearing in Figures 1d and 1e.
6. In Table 1, the Yplus =1.7, why the value is not less than 1.0 since no wall function is used?
7. In line 174, the citation [27] did not set the inlet velocity for forward flight. It was a paper that studied the hovering state of a helicopter rotor.
8. In line 190, the author did not give the value of Gamma yet.
9. Please clarify the test conditions of the grid sensitivity analysis. What are the pitch angle and rotational speed?
10. Actually, it is weird to place the main rotor geometry parameters in the experiment part. I suggest the author put the model information at the beginning of section 2.
11. The format of the reference part needs to be unified. The journal name in some references was missing.
It still needs to improve further, since there are some errors in the content yet.
Author Response
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Author Response File: Author Response.docx
Round 3
Reviewer 4 Report
My comments about this paper were well addressed, except for the comment 7. However, I think this paper could published in the present form.
Only two points I have to point out.
1. Line 180, which related to the comment 7, I suggest authors should reconsider the sentence “The inlet velocity was set to 10 m/s for forward flight condition to align with the conditions of a wind tunnel experiment [26].” carefully. As I mentioned in comment 7, the reference [26] was mainly about the rotor in hover condition, it didn't set the forward flight condition. It is weird to say that the 10m/s inlet velocity aligns with the wind tunnel condition in reference [26].
2. Line 366, please check the table here is Table 3 or Table 4?
It could be improved further yet.
Author Response
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Author Response File: Author Response.docx
