Aerodynamic Drag Reduction on Speed Skating Helmet by Surface Structures

Round 1

Reviewer 1 Report

See attached file

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

This is an interesting paper comparing both CFD and experimental results to investigate drag reduction for speed skating. It is generally well written, concise, yet good on explaining the CFD and experimental setup, and results. It adds interesting insight as to the aerodynamic performance of speed skating helmets.

* specify what CFD code was used, was it commercial? Custom?

* you mention wind tunnel turbulence values, any comment on CFD inlet turbulence values chosen?

* it would be good to include a sentence or two regarding the choice of boundary layer mesh, how many layers, how thick, etc.

* Fig 11-14: good figures, analysis, and explanations

* Fig 14 caption does not explain what d, e, and f are. You may want to talk a little bit about the change in surface streamline directions (oil flow) that you show in d, e, and f between the original and the riblet/bumped models. Clearly the riblets on the sides change the predominant flow direction there.

Overall an interesting paper I enjoyed reading.

 

Misc typos:

*various small typos, including extra/insufficient spaces (often near [] brackets where references are cited)

*p2, line 62 “separate point” –> “separation point”, also line 70 etc

*p2, line 66-67, grammar “attention to drag the reduction method”

*p2, line 87 “rectangular box” is probably better than “rectangular prim”

* Fig 9 “Origin” à “Original”

* p9, line 218, “high”

*p10, line 241 font in “Fluid Field Profile” F and P

* etc more misc grammatical errors/typos

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

The work examined the aerodynamic drag for the skating helmets. Although not surprising, the work is overall interesting. However, the referee has the following concerns:

1. Both the CFD and experiments are presented in the manuscript, but the connection between them is rather weak.

2. For LES, details about the numerical scheme should be provided. For example, what is the solver, and what is the mesh distribution; and, in addition, what is the boundary condition for the ground? How has the effect of tiny riblet/bump been resolved using LES.

3. How are the drags measured in experiments, and what is the uncertainty level?

4. Figure 14(d-f) is never referenced nor discussed.

 

 

 

Author Response

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Author Response File: Author Response.docx

Reviewer 4 Report

The authors have investigated the Aerodynamic Drag Reduction on Speed Skating Helmet. My suggestions are given below:

1) List all the assumptions used in numerical simulation.

2) Include whether it is a steady or unsteady simulation?

3) Include the convergence criteria chosen for numerical simulation.

4) The boundary conditions are not clear.

5) How are the CFD results validated?

 

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

The revision is satisfactory, and I recommend its publication.