Analysis of Aerodynamic Characteristics of Propeller Systems Based on Martian Atmospheric Environment

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

I have found the manuscript quite interesting. I have some comments that I understand could improve the quality of the final paper:

1. Please add more context to the references. As a first example, look at references 1 and 2: what do you find interesting and relevant to your manuscript about them? Yes, they are about space (and Mars!) exploration, but what do they say? Instead of writing something like "(...) human living space [1,2]", please write something like "(...) human living space. Indeed, Petritoli and Leccese [1] blahblahblah. Also, Wu and Yu [2] blahblahblah."

2. Page 2, line 52: I think that the correct wording is "compressible flow conditions".

3. This one is just about style. Page 3, line 98: much worse in what sense?

4. Page 3: endurance time sounds a bit redundant to me. Why not just endurance?

5. Page 3: I think that "Gas constant" is much more standard than "Atmospheric constant".

6. Page 4: "string" should be "chord".

7. Page 4, line 144: 10⁴

8. Page 4: there are, indeed, interesting research works about low Reynolds propeller performance. I think that you should cite some of the works from UIUC (not affiliated with them!). Look for Brandt, Deters, Ananda, Dantsker and Selig. I agree that their experiments do not fully cover what you would expect to have on Mars, but they are some of the closest ones.

9. Page 5: 104 again.

10. Page 5: inducted should be induced.

11. Page 5: element ring should be circulation.

12. Page 6: induced pitch should be induced angle of attack.

13. Page 6: again, ring should be circulation.

14. Page 6: torsion should be twist.

15. Page 7: integralizing should be integrating.

16. Page 7: there is something missing in line 229.

17. Page 8: this is maybe completely valid, but I would call equation 16 "unsteady, compressible, potential flow equation".

18. Always use normal fonts for units. Italics should only be used with variables.

19. Page 8: why the blade tip Mach number limit is equal to 0.85? I understand that it is to avoid most of the transonic effects (like flow separation due to shockwave-boundary layer intereaction and subsequent extreme drag and loss of lift), but it is not explained in the text.

20. Page 9: mesh encrypted? It is the first time that I have read that term. What does it mean? Could it be a translation error?

21. The mesh independence study is not well performed. Although it is common to do like in this manuscript, the proper way of doing a mesh independence study is to provide some estimation of the uncertainty of the results. For that, there are well proven standard methods, such as the grid convergence index (GCI).

22. Are the authors sure that they have simulated everything using potential flow with Fluent?

23. What are the units of the pressure shown in Figure 7?

24. Page 10. What is PMI? I know that it is polymethacrylimide, but please explain it in the text.

25. Page 12: please explain all the terms in the equations.

26. Page 16: what are the sensors that the authors used?

27. Page 17: the authors imply that their simulations had flow separation, which is not possible to simulate using just a potential flow solver. Indeed, in Fluent, you can solve Euler's equations, which are not exactly potential flow and do not solve the equations that the authors showed. So I suppose that the simulations where different. In that case: what equations were actually solved?

28. Usually, when talking about propellers, equation 31 is the thrust coefficient.

29. Is the power used for the power coefficient measured with a torque meter and the rotational speed of the propeller or is it the electric power? If it is the electric power, it also includes the electric losses in the motor, wirings and electronic speed controller.

30. Page 20: what is virtual displacement?

31. Page 20: I wouldn't trust the numerical results either, unless the authors can show more evidence about their quality and accuracy.

32. Finally, regarding the figures: when showing the experimental and numerical results side by side, it can sometimes be difficult to compare them. Maybe it is worth trying to put both experimental and numerical results in the same plot. Maybe not, because there are too many data points to show, but I still it is worth trying.

Comments on the Quality of English Language

There are some minor issues with some naming conventions and wrong wording. Such is the case of using "ring" instead of "circulation", "string" instead of "chord" or "integralizing" instead of "integrating". Please correct them all before resubmitting.

Author Response

请参阅附件。

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

The paper is focused to the moder and interesting theme of propeller design for Mars. It multidisciplinary and contains aerodynamic design of the propeller, structural analysis, CFD analysis and experimental testing. The results of CFD analysis are compared with experimental results. 

 

I appreciate the complexity of the approach but I have several important issuses that have to be corrected:

1) The nomenclature shoul be corrected so that standard names are used, e.g. FM is usually figure of merit not quality factor. You use lift the coefficient cl instead of the thrust coefficient cT. Lift coefficient fo the rotors is used in different meaning (local lift coefficient on the blade).

2) Equation (32) and (31) - your formulas are not consistent, they must both contain 3600 (if you use RPM) or not (if you use RPS), the combination is not possible.

3) Experimental results look very strange (Figs. 14b and 15b). It looks like influence of the vacuum chamber. This have to be explained. I see two possible solutions - you can repeat the tests on the air in sufficient big space (or outdoors) to check if you see the same phenomena. Or you can do the CFD analysis not only for the small control volume, but you add the whole volume of the vacuum chamber.

Fig. 9 a contains deformation of the propeller, but you should specify which deformation - it looks like deflection in axial direction, but hte caption is not clear.

Author Response

Please see the attachment.

Author Response File: Author Response.docx