Optimal Design of Computational Fluid Dynamics: Numerical Calculation and Simulation Analysis of Windage Power Losses in the Aviation

Round 1

Reviewer 1 Report

The paper fits the journal scope and I enjoyed reviewing it. However, there are essential issues that must be corrected. Thus, I recommend a major revision.

1. The paper is written in good English. However, there are some errors that must be eliminated e.g., hyphenation: calcu-lation (page 2 line 80), ef-fective (page 2 line 78). The authors are advised to read the paper carefully once again to eliminate those errors.
2. Please provide technical details of the hardware used (Super Cloud Computing Center)
3. Was parameters uncertainty (e.g., geometrical) taken into account? If yes, provide results showing their influences. If this was not done, at least provide a qualitative discussion.
4. Please provide more details on the computational domain. What about mesh sensitivity check? What was the mesh size, and what elements were used?
5. Bibliography is inconsistent and not written according to MDPI standards (e.g., author names written only with capital letters)
6. Author contributions are not filled

For now, this is all for me. I hope that the authors will respond to all my comments.

Author Response

Dear reviewer

Thank you for taking the time and effort to review our manuscript. All your questions were answered and the revised changes are highlighted on the manuscript in red color. We are thankful for the comprehensive and valuable suggestions to improve the quality of our work.

Author Response File: Author Response.pdf

Reviewer 2 Report

Unfortunately, I consider that the manuscript cannot be accepted for publication since it has serious flaws related to the CFD model implemented:

1. The authors mention that the Reynolds number is in the order of 10⁶, if this is true then using the kinematic viscosity of air at standard conditions (not even mentioned in the manuscript) then the characteristic velocity is in the order of 10 m/s. If this is true, then wxr=10m/s and if w=20000 r/min then the radius of the driving gear is in the order of mm, how can this be possible?
2. Let’s assume that the driving gear diameter is in the order of 1x10^-1 m then the characteristic velocity would be in the order of 1x10² m/s so that the Mach number must be in the order of 0.3 to 1. For this condition the assumption of incompressible flow is completely invalid. This estimation is in agreement with figure 8 in which the velocity of the air is in the order of hundreds of m/s.
3. Since the Mach number is so high, then isothermal condition can not be used so that the energy equation must be solved and a model for the variation of the physical properties of the air should be included.
4. The abstract is quite confusing since it is mentioned the use of a two-phase flow model (oil-air), but this is not the case.
5. Equation 8 does not correspond to an incompressible assumption.
6. Details of the size of the domain of the air and the boundary conditions of this domain should be clearly stated and supported.
7. Since the velocity of the air close to the surface of the gear is so high, then a correct discretization in this area should be done. This can not be done with only tetrahedral elements since the quality of the mesh (not shown or even discussed) would be too low.
8. Convergence analysis results must be clearly shown.
9. Details of the mesh should be shown, especially close to the gear surface.
10. According to the authors only 0.004 s were simulated, this corresponds to only 1.3 turns in the driving gear. Typically, this kind of problems require more turns in order to achieve a correct convergence especially for the estimation of the torque.

Author Response

Dear reviewer

Thank you for taking the time and effort to review our manuscript. All your questions were answered and the revised changes are highlighted on the manuscript in red color. We are thankful for the comprehensive and valuable suggestions to improve the quality of our work.

Author Response File: Author Response.pdf

Reviewer 3 Report

The reviewed article concerns the multi-objective optimization on windage losses in the aviation. The authors used CFD method. The authors carefully planned the research plan and then correctly implemented it. The adopted research goal has been achieved. The research topic is interesting for the readers. I propose to accept the article after completing and clarifying a few issues: 

- Please consider clarifying the title of the article. In its present form, it is too generally related to the research carried out. 
- The literature review and research gap are presented at a decent level. However, it is worth specifying the purpose of the research more precisely and emphasizing the potential practical use of the research results. 
- It is worthwhile to justify the choice of the turbulence model. 
- Please describe in more detail the analysis of the independence and convergence of the mesh. It is important due to the lack of the possibility to validate the research results.   
- The adopted boundary conditions should be described in more detail in chapter 3.3. 
- Chapters 4 and 5 are decently drafted - however, they lack elements of discussion. 
-  Chapter 6 is very general. The summary should contain more "measurable" information (expressed in numerical values) obtained from the research process. It is also worth mentioning the practical application of the research results.
- Editing errors and typos occur in several places.

Author Response

Dear reviewer

Thank you for taking the time and effort to review our manuscript. All your questions were answered and the revised changes are highlighted on the manuscript in red color. We are thankful for the comprehensive and valuable suggestions to improve the quality of our work.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Thank you for providing a response to all my comments.

Reviewer 3 Report

I propose to accept the article.