Experimental Analysis of the Influence of Aeration in the Energy Dissipation of Supercritical Channel Flows

Round 1

Reviewer 1 Report

Water Type Article

Title: Experimental analysis of the influence of aeration in the energy dissipation of supercritical channel flows

The present manuscript conducts laboratory experiment in high-speed supercritical flows with high concentration of air bubbles. I respect authors providing valuable experimental data, because it is very hard to obtain velocity and concentration profiles in such violent condition. Thus the present database is useful for hydraulic engineers.

However, there are some doubts to understand the manuscript.

 In my opinion, it requires following revision before ready for publication. I hope authors prepare intensively revised version to be certainly of use for readers.

My specific comments are as follows;

  Specific comments -

1 Table1:  Is Vin cross-sectional averaged value measred by the Pitot tube?

Air bubbles influence some reduction of velocity measurement accuracy?

2.Fig.7: Authors assert bubbles increase flow velocity. This is very interesting.

 How bubbles accerelates mainstream?   What kind of forces act on streamwise current?

3.Fig.7: Why the concentration becomes zero at the flume bottom?

4.Fig.7: Generally speaking, maximum velocity appears near the free-surface without secondary currents.

 Could you show the mechanism in which we can see the peak velocity near the bottom?

5.Table3: I think that "n" depends on only material of flume bottom. I ask you some comments about this.

6.Fig.13 and Eq.(3): why the slope of Eq.(3) is positive?  

 In Fig.13, Manning's roughness coefficient decreases with CM.

7.Line 229-230: Authours conculude that higher concentration implies lower friction head loss.

But Figs.7 to 10 show the larger velocity are observed near the bottom with larger concentration.

That is to say, the higher concentration generates larger velocity shear, i.e., larger friction loss.

Authors should explain about this topic.

Author Response

Hydraulic Laboratory of the Hydrographical Study Centre, CEDEX, Ministry of Public Works and Transport, Madrid, Spain, March 13^th

Dear Editor,

Thank you very much for sending us the reviewers’ reports on our manuscript “Experimental analysis of the influence of aeration in the energy dissipation of supercritical channel flows.” (Ref.: Water- 452387).

Enclosed please find our reply (in italics). The original comments are boldfaced and the corresponding revised text is presented in standard font with the modifications underlined. We have thoroughly revised the original manuscript with all suggestions in mind.

We wish to thank you and the Reviewers for helping us to improve the manuscript and hope you will find the revised version acceptable for publication in Water.

Sincerely,

         Juan José Rebollo

Author Response File: Author Response.pdf

Reviewer 2 Report

The authors present a very interesting and useful manuscript that deserves to be published.  My comments aim at strengthening the manuscript.

General comments:

Would it be useful to compare velocity profiles with the case when there is zero air entering the spillway chute?

As air concentration typically increases with distance down a spillway chute, does Manning's n vary along a spillway chute, especially a long chute.

When water depth increases with discharge down a channel having smooth sidewalls, would not the value of Manning's n not increase anyway.  I see no discussion of sidewall correction in the analysis of the flows.

Are the results of this study applicable to stepped spillways, which are becoming very common?

Minor comments (mainly editorial)

the opening two sentences of the Introduction are rather terse (and bland) and should be linked so as to express a major motivation for conducting the present study.

Line 52:  Influence of aeration on what?  The authors should state the objective more pointedly.

Line 54: Are these values of Froude number representative of spillway flows.  If so, the authors should say so.

Fig 1(b).  Some labels would help the reader identify the spillway.  Are there several spillways in this picture?

Figs 7-11.  I encourage the authors to define "H" in the figure.  The figure captions should mention "H".  Actually, can these figures be combined as a set of figures, as they present very similar information?

Line 148:  I suggest changing "affects to" to "extends to".

Eq (3): Care should be taken so that "(C_M)" is not mistaken for a variable on the left side of this equation.

Line 232: Where is the "dimensional analysis"?  The manuscript presents no dimensional analysis.  Could the authors include a brief dimensional analysis, at least identifying the important parameters varied in their experiments.  I imagine the ratio Qa/Qw would be important.  How does this parameter relate to air concentration?

Author Response

Hydraulic Laboratory of the Hydrographical Study Centre, CEDEX, Ministry of Public Works and Transport, Madrid, Spain, March 13^th

Dear Editor,

Thank you very much for sending us the reviewers’ reports on our manuscript “Experimental analysis of the influence of aeration in the energy dissipation of supercritical channel flows.” (Ref.: Water- 452387).

Enclosed please find our reply (in italics). The original comments are boldfaced and the corresponding revised text is presented in standard font with the modifications underlined. We have thoroughly revised the original manuscript with all suggestions in mind.

We wish to thank you and the Reviewers for helping us to improve the manuscript and hope you will find the revised version acceptable for publication in Water.

Sincerely,

         Juan José Rebollo

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Authors have improved and revised very carefully according to my all comments.

Hence, this manuscript can be published.