Analysis of Flow Characteristics and Effects of Turbulence Models for the Butterfly Valve

Round 1

Reviewer 1 Report

See attached file　

Comments for author File: Comments.pdf

Author Response

This paper has been reconstructed as the reviewers’ suggestion. We, the authors, really appreciate the reviewers’ helpful comments. We feel that this paper has become more rigorous and well-constructed after implementing the suggested parts in the manuscript. The modified or added parts are highlighted in yellow background in the manuscript.

Reviewer 2 Report

The paper is interesting. The structure of the paper is correct. Nevertheless, some aspects of the paper should be revised and improved:

• The manuscript requires careful attention to presentation. The text must be carefully checked in terms of styles and formatting for symbols, equations, figures, tables and references. For example, on page 4, "buttery" instead of "butterfly", and so on.
• The authors should review the nomenclature. It is not complete.
• I think it would be interesting to add a photo of the butterfly valves used in the research.
• Page 10: How has the valve disc been modelled in CFD? A simple line?
• Page 11: “This means that the flow coefficients are dependent on the flow configurations given by the actual flow path resulting from changing the disk opening of the valve which determine the effective flow region to control flow behavior in the valve”. The authors should better explain this sentence.
• Page 11: “The results in Fig. 3 show that discrepancies varied with valve size, which means that one turbulence model did not lead to precise numerical predictions for all valve sizes”. Does this have any explanation? The authors should try to justify this statement.
• Figure 3: I think it would be interesting if the size of the valves (DN80, DN262 and DN400) appeared in the graphs.
• Page 15: “As the valve size and disc opening decreased, a relatively smaller effective flow region with a relatively smaller area between the disc and valve wall caused a large pressure drop and velocity increase, which could increase turbulence. Increasing turbulence represented by turbulence intensities could cause lots of discrepancies between turbulence models, especially in areas with large pressure drop and sharp velocity increase”. The authors should better explain this sentence.
• In section 5.1 there is a lot of information. It would be interesting to add at the end of the section a brief summary with the main conclusions of the sensitivity analysis of two-equation k-epsilon model.
• Page 27: “From sensitivity analysis results, it can be suggested that errors in numerical calculations should be checked for turbulence constants with respect to the flow characteristics when using each the turbulence models”. The authors should better explain this sentence.
• In section 5.2 there is a lot of information. It would be interesting to add at the end of the section a brief summary with the main conclusions of the sensitivity analysis of two-equation k-omega model.
• Conclusions: Do any of the three turbulence models analysed have advantages over the others? This should appear in the conclusions.
• Conclusions: Regarding the analysis of turbulence models, what are the future developments of the research presented in this paper?
• References: The authors should review the format of the bibliographic references.

To conclude, in my opinion, the paper can be accepted with modifications, mainly related to complete and clarify some issues.

Author Response

This paper has been reconstructed as the reviewers’ suggestion. We, the authors, really appreciate the reviewers’ helpful comments. We feel that this paper has become more rigorous and well-constructed after implementing the suggested parts in the manuscript. The modified or added parts are highlighted in yellow background in the manuscript.

Author Response File: Author Response.doc

Reviewer 3 Report

Analysis of Flow Characteristics and Effects of Turbulence Models for the Butterfly Valve

The authors numerically study the the flow characteristics of butterfly valves with different sizes under different valve opening positions using the commercial CFD code CFX. The performance of two-equation turbulence models (k-w, k-e, SST) were assessed to determine the accuracy of numerical solutions when compared to experimental data from the literature. It is a good study and can be considered for publication. However, there are a few issues that need to be resolved before acceptance. 

1. Your introduction section needs to be improved by reviewing more of the previously carried out research in butterfly and other valves using CFD. furthermore, you should clarify which of the turbulence models are most frequently employed.
2. What value did you assign to N1 in equation 15? Please express the equation after substituting the specific gravity and N1 so that it is clear to the reader as the value of the constant has to be 11.56 if kPa and m3/h are used for DP and Gf respectively. 
3. As valves are sized by the flow coefficient Cv,  the effect of your turbulence models on pressure drop and this quantity has not been studied. For this paper to be useful, it needs to be done.
4. Your velocity profiles at 10x/y are not as expected for a fully developed turbulent flow. It appears the development length after the valve is not sufficient. The authors need to comment on this. 
5. kindly improve the quality of your images which are mostly blurry
6. Please check varying spacing and proofread to address a few typos here and there. For example a mixture of US and UK spellings have been used (e.g. disk and disc) which need to be made consistent. 

Author Response

This paper has been reconstructed as the reviewers’ suggestion. We, the authors, really appreciate the reviewers’ helpful comments. We feel that this paper has become more rigorous and well-constructed after implementing the suggested parts in the manuscript. The modified or added parts are highlighted in yellow background in the manuscript.

Author Response File: Author Response.doc

Round 2

Reviewer 1 Report

See attached file.

Comments for author File: Comments.pdf

Author Response

This paper has been reconstructed as the reviewers’ suggestion. We, the authors, really appreciate the reviewers’ helpful comments. We feel that this paper has become more rigorous and well-constructed after implementing the suggested parts in the manuscript. The modified or added parts are highlighted in yellow background in the manuscript.

Author Response File: Author Response.doc

Reviewer 2 Report

The authors have made changes and the paper has been improved. However, there are several recommendations that have not been considered:

• The manuscript requires careful attention to presentation. The text must be carefully checked in terms of styles and formatting for symbols, equations, figures, tables and references. For example, on page 4, "buttery" instead of "butterfly", and so on.
• The authors should review the nomenclature. It is not complete.
• I think it would be interesting to add a photo of the butterfly valves used in the research.
• Page 10: How has the valve disc been modelled in CFD? A simple line?
• Conclusions: Do any of the three turbulence models analysed have advantages over the others? This should appear in the conclusions.
• References: The authors should review the format of the bibliographic references.

To conclude, in my opinion, the paper can be accepted with modifications, mainly related to improving the presentation of the paper and reviewing the nomenclature, conclusions and references.

Author Response

This paper has been reconstructed as the reviewers’ suggestion. We, the authors, really appreciate the reviewers’ helpful comments. We feel that this paper has become more rigorous and well-constructed after implementing the suggested parts in the manuscript. The modified or added parts are highlighted in yellow background in the manuscript.

Author Response File: Author Response.doc

Reviewer 3 Report

the authors have revised the document based on some and left other comments partly or completely unattended to and the reviewer is of the opinion the paper will not be of much use in the current version if published. Specifically:

• the comment made on effect of turbulence models on pressure drop and Cv was essentially ignored with the authors answering with an irrelevant reference to section 4.2 and fig. 7 which show something completely different. The authors need to show this effect as designers are mostly concerned about Cv and DP for sizing and estimating pumping requirements. 
• still occurrences of both "disc" and "disk". Please check again and correct. 
• most of the images are still of rather poor quality and should be improved. 

Author Response

This paper has been reconstructed as the reviewers’ suggestion. We, the authors, really appreciate the reviewers’ helpful comments. We feel that this paper has become more rigorous and well-constructed after implementing the suggested parts in the manuscript. The modified or added parts are highlighted in yellow background in the manuscript.

Author Response File: Author Response.doc

Round 3

Reviewer 1 Report

I confirmed that Fig.2 and section 4.1 were revised.

But my question “How numerical values of differences for the flow coefficient are calculated?” is not answered. The reason for this question is that I cannot understand the word "differences for the flow coefficient. When I read the 1st version manuscript, I thought this means the difference between the experimental results and the simulation results. So I cannot understand how the numerical values in Table 1 are calculated. But it came to mind today that the differences for the flow coefficient might means only the difference of numerical results, e.g. between cell number 250,000 and 350,000.  If so, Table 1 is unnecessary. The mesh dependency shown in Table 1 is clear from FIg.2. If you use Table 1, you should show the criteria for judging convergence of numerical simulation. For the case of Fig.2 and Table1, it seems that the critical difference is 1%.

Author Response

Thanks for your kind advice

At first, I don't understand your intention to show the difference between them.

With your kind explanation, I also figure out your intension.

First time I show the difference for the flow coefficient means difference of numerical results between element numbers. So, I decided to delete Table 1 with your comments.

Thank you again for your kind comments.

Author Response File: Author Response.doc

Reviewer 2 Report

After this last review, the authors have made changes and the paper has been improved significantly. The paper can be published.

Author Response

We, the authors, really appreciate the reviewers’ helpful comments.

We feel that this paper has become more rigorous and well-constructed after implementing the suggested parts in the manuscript. 

Thank you so much.

Round 4

Reviewer 1 Report

There is no more comment.