Investigation of the Time Resolution Set Up Used to Compute the Full Load Vortex Rope in a Francis Turbine

Round 1

Reviewer 1 Report

Dear Authors,

I have found in my opinion a lot of inaccuracies and ambiguities. I presented it in the original pdf file. Please, see attachment. Below I present only general remarks as the most important points concerning the quality of paper.

Chapter 2. Authors should present the cross-section of the turbine with main dimensions for the reader’s convenience to be able to compare with the other machines. Generally, I think the information about prototype machine (we know only the power 444MW and nothing else) is quite poor. What is the head, rotational speed, etc.? Especially, if Authors discuss about Thoma number tailwater level should be presented.

Chapter 2. Present specific speed definition. In the Research Centers different definitions are used.

L80. “The y+ value does not exceed 85 and the averaged value over each solid walls is lower than 20”. Earlier Authors mentioned about the usage of (k-w) SST model. This model is rather demanding taking into account the mesh requirements. In order to properly model the boundary layer minimum value of Y+ should be below 3 (with three grid nodes below 11). This is quite confusing if the results are reliable. Can Authors justify and comment it in paper?

L105. The divergence of Case 1 causes that some time steps earlier the flow becomes affected by numerical problems. Some results become then unreal. I think it is extremely important to comment it in paper.

L111. “Regarding the efficiency, the torque factor and the speed factor, the differences between the simulations are around 1.5%”. How do Authors justify the grid independence especially when 1^st order scheme for volume fraction was used. Please refer to that in paper.

General remark to Chapter 3. I do not see any discussion on CFL number. Especially, it is quite important when Authors stated that in Case 1 the calculations diverged. As it might be caused by too high number of CFL, why did Authors apply CFL = 80 in Cases 1 and 2 and why =<2 in Case 3? Some discussion according all mentioned points should be presented.

Figure 8. How do Authors explain the difference between numerical and experimental results (they are highly periodical with clearly visible peaks oppositely to numerical results)?

Conclusions. Expand ‘Conclusions’ regarding comparison with experimental results. They are too poor now.

General remark. State clearly what is a novelty of the paper. I think this is missing.

English requires some polishing. I have found some mistakes.

With best regards

Comments for author File: Comments.pdf

Author Response

The response to the reviewer is in the attached PDF file.

Author Response File: Author Response.pdf

Reviewer 2 Report

Dear authors of the paper "Investigation of the time resolution set up used to compute the full load vortex rope in a Francis Turbine".

In order to increase the paper visibility, please find below my recommendations:

1. Introduction - is clear and describes very well the case

Please modify the text for:

• line 25 "Best Efficiency Point" with "Best Efficiency Point (BEP)"
• line 34, please corect ... various studies have be performed ...

3. Numerical settings

• line 90,please corect ... and has been validate against ...
• for Figure 2, is good to add some text with the main components of the investigated turbine in numerical simulation. Please add some supplementary pictures with zoom on the mesh in the interest areas, such as runner or the draft tube.

4. Results

• on the point 4.2. Local pressure, lines 133-137, supplementary with the pressure probe description and localisation, you can name each probe and put these names also on Figure 7.
• as a general comment regarding the article, please arrange the pictures as close as possible to the text where is described.
• the legend from Figure 3 is not readable.
• for Figure 4 - can you add the values from the experimental analysis, even if you have mean values.
• the comparison between experiment and simulation (from Figure 9) is commented only for frequency. Please explain once again at the end of chapter 4, why is this difference in magnitude and what can be done to surprise much better the experimental case.

Author Response

The response to the reviewer is in the attached PDF file

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Dear Authors

You did a lot to improve the quality of paper and I really appreciate it. I hope my indications will improve the quality of your paper. My only intention when reviewing is always to improve the quality. Please see below what I see in paper to be missing and in my opinion is important. Another lacks are rather small and meaningless.

My main concern is as follows. I know that Authors would like some details of prototype to be hidden. I understand it but the knowledge of values e.g. rotational speed, characteristic dimensions, head does not reveal the details of prototype machine. This just means that numerical results in which abovementioned values are introduced cannot be interpreted by a wide researchers of hydropower. I think in such a case the contents of paper are untold and unfinished. It is Your will, however I strongly encourage you to introduce some of abovementioned values in paper.

I still see some English mistakes. E.g. in the new added text I have noticed: “has been done and publish”, “as shown on figure”, “The results described in the previous section makes appear”, “simulations Case 2 and Case 3 does not show”. Please, make correction with the use of native English speaker.

With the best regards

Author Response

The answers to the reviewer's comments are in the attached PDF file

Author Response File: Author Response.pdf