Oil Cavitation Morphology Analysis of Textured Cylindrical Rotating Friction Pair on Circular-Disk End Faces

Round 1

Reviewer 1 Report

1) The use of English language can be improved, for example: lines 29, 30, 36, 44, 45, 47, 48, 54, 59, 65, 118, 169, 188, 203, 206, 282, 288, 359, 383

2) What is the reference to what is said between the lines 40 to 48?

3) Obviously there is no absolute negative pressure. Better explain the negative relative pressure found by Euler.

4) What is the reference to what is said between the lines 48 to 51?

5) What is the reference of Figure 1? Add this information to the figure caption.

6) Does reference [25] relate to cavitation? If so, in addition to reporting the appearance of secondary flows, talk about cavitation in the reference.

7) The same for references [26 to 28]. Is there cavitation in the secondary flows? Explain the relationship of these flows with cavitation.

8) The same for reference [30]: what is the relation between cabitation and unstable boundary layers? Put it in the text.

9) Figure 3 is very small, so it is difficult to see the radius "R" inside the bubble. I suggest enlarging the figure, or showing the "R" in a more easily visible way.

10) Just an opinion, the authors can feel free to follow this recommendation or not: perhaps a quick explanation of the non-homogeneous flow model, in comparison with the homogeneous model, can make the text more interesting.

11) What is the reference for Figure 3, for equations (1) to (3) and for the explanation of the homogeneous flow model? The CFX documentation itself? To quote.

12) Lines 131 and 132: the turbulence model is important for turbulent flows (high values of Reynolds number), with or without vortexes. Improve your explanation of why to use the turbulence model. It is not simply because there are vortexes.

13) On line 155, it's equation (11) and not (6). Explain the validity of ignoring the second derivative and the surface tension term.

14) Explain equation (15) better: Is Rb an average radius representative of the Nb bubbles, or do all bubbles have a constant radius equal to Rb (unlikely)?

15) Explain better why the values quoted in line 170 were used.

16) In section 2, the equations of the homogeneous flow model, of the turbulence model and of the cavitation model were shown and explained. However, the Fluid Mechanics equations were not shown. Show these equations, or at least quote them and explain them briefly in the text, to close the problem.

17) Figures 4 and 5 can be enlarged to allow a better view, especially Figure 5.

18) The same for Figure 6.

19) Lines 185 to 190: why were these boundary condition values used? Explain better: do they correspond with the experimental condition? Is the outlet static pressure absolute (zero indicating vacuum) or relative (indicate the reference pressure value)?

20) Lines 191 to 195: why were these time values used? Explain why 0.1 s of total time is sufficient to simulate the desired phenomena. Also, show the time step dependence study showing that the value of 0.001 s is sufficient to capture the transient phenomena in question.

21) Figure 6 and its caption are on separate pages.

22) Create a subsection (into section 3) to show and explain which numerical scheme was used. Are they at least second-order discretrization schemes?

23) Figure 7 is too small, not being possible to see the mesh details.

24) Line 211: explain whether there are guarantees that the grid independence study carried out in steady state is valid for the transient state?

25) Emphasize in the text that, therefore, the mesh of 1,607,374 elements was used. The total number of elements is critical information for the reader.

26) What is the reference of equation (18)? The CFX documentation itself? To quote.

27) Line 229: What is the vapor fraction value for the 3.205% setting?

28) Figures 9 to 11 are too small, making it difficult to visualize and interpret the results. The same for figures 12 and 13.

29) What is the total time used in the simulations and in which computer model/type? Present a representative figure of the decayment of residues in relation to the different simulated cases.

30) Avoid using first person in the text, line 281 and others.

31) Line 283: Explain why the saturation pressure is 1000 Pa?

32) Table 4 is not cited and explained in the text.

33) With the explanation and figures provided, it is difficult to understand the experimental apparatus and the experimental procedure.

34) There are two Figures "21".

35) Were the rotations used in the experiment (300 to 1000 rpm) and in the simulations (1000 to 6000 rpm) different? It wasn't clear. To explain better.

Author Response

Dear Reviewer,

The authors are grateful to you for some useful and important comments for our paper submitted to Machines. You gave very detailed and professional revisions that will help improve the quality of my article. The manuscript ID is machines -1956427. I have documented the revision process in the attached document in order to respond to your review comments in greater detail.

Yours sincerely!

Corresponding author: Name: Junyu Sun

Author Response File: Author Response.pdf

Reviewer 2 Report

1. In the table. 2, the units of measurement are not indicated, so it is not clear how the model was simplified.

2. Why are these sizes of micro-dimples chosen in Section 3? How do they relate to real products?

3. Simulation should be carried out at 1000, 1500, and 3000 rpm, which is more realistic in practice.

4. Section 5 does not specify the dimensions of the friction disc and the dimensions of the holes on it.

5. When modeling in section 4, the rotation speed was 6000rpm, and in section 5 it was 350-1050rpm, what is the relationship?

6. Analysis of the intensity of cavitation should be carried out based on the linear velocity of the disk.

7. The figures are of poor quality.

Author Response

Dear Reviewer,

The authors are grateful to you for some useful and important comments for our paper submitted to Machines. You gave very detailed and professional revisions that will help improve the quality of my article. The manuscript ID is machines -1956427. To more clearly document the process of revising my paper based on your review comments, I have included more details in the attachment for your ease of reading.

Thank you again for your suggestions and professional revisions, which will greatly improve the quality of the paper.

Yours sincerely!

Corresponding author: Name: Junyu Sun

E-mail: [email protected]

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

After the changes implemented, I recommend the publication.