Numerical Study on the Flow and Structural Characteristics of a Large High Head Prototype Pump-Turbine under Different Operating Conditions

Round 1

Reviewer 1 Report

In "Conclusion" section, the authors should give the main results rather than all results.

 

The paper should be carefully revised for punctuation, grammar, spelling mistakes and sentences structuring.

 

The Abstract should contain answers to the following questions: What problem was studied and why is it important? What methods were used? What are the important results? What conclusions can be drawn from the results? What is the novelty of the work and where does it go beyond previous efforts in the literature? Add the main findings and objective of the current study in the abstract.

 

It is necessary to introduced the parameters of all equations in first usage. The nomenclature is not adequate in this regard.

 

The authors should report some of the important findings and results in highlights.

 

All abbreviation that appears for the first time should be written in its full name

 

The innovation of this paper is not prominent. In fact, some scholars have made corresponding analysis of the problems studied in this paper.

 

Introduction ignored important contributions in this research area. Please at least add 10 more references in 2022 and 2023.

Good

Author Response

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Reviewer 2 Report

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Comments for author File: Comments.pdf

Author Response

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Reviewer 3 Report

The authors presented a 3D CFD analysis coupled to structural analysis for a turbomachine devise. Comments and questions are shown below:

1- The contribution of the study is weak. The authors presented the results using a software but they didn't tell readers what they are trying reach. State your contribution properly. 

2- The abstract is poor. The abstract is the gate to your manuscript. It should contain answers to the following questions: What problem was studied and why is it important? What methods were used? What are the important results? What conclusions can be drawn from the results? What is the novelty of the work and where does it go beyond previous efforts in the literature?

3- The literature study is insufficient. You should more recent studies related to your topic.

4- Avoid lumping references such as [1-4], [5-10]. You should either stick to one reference of talk briefly about each cited reference.

5- line 78, ''Since the high overall stiffness of the unit structure, the influence ..''. This sentence is not clear.

6- line 92-93, '' ....consists of the spiral case, guide vanes, stay vanes, runner, draft tube, crown chamber, band chamber, and balance pipes'' describe the function of each component. 

7- Are the data in lines 95-98 (Table 1) based on experimental analysis? Why these values specifically? 

8- Improve the bounds of the vertical axis in Fig. 3 and Fig. 5. i.e the minimum bound could be 75 or 80% in Fig. 3 to clearly visualize the results.

9- The manuscript contains typo and grammatical mistakes. Revise carefully.

 

The manuscript contains typo and grammatical mistakes. Revise carefully

Author Response

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Reviewer 4 Report

The paper presents the results of simulation of transient flow and vibration using a rationally built unidirectional FSI model. Due to the small absolute deformations of the elements of the pump-turbine mechanical elements, their effect on the flow structure is negligible. On the other hand, pressure distributions that vary both in time and space, generate forces that excite mechanical components to vibration.

The equivalent von Mises stress is the correct measure of the load on the mechanical components of the pump-turbine. Only the vibration of the pump-turbine housing is analyzed.

Line 97 duplicated word "runner" exists.

Suggested enlargement of drawings. They contain many details visible accurately only under magnification.

Fluid flow.

The surface grid shown in Figure 2 is sensibly dense. The mesh used to discretize the computational area of the flow sensibly dense at the leading and trailing edges of the blades. In contrast, it does not include a dense mesh for the near-wall layer. At the pressures present in the pump-turbine ( 54 bars), pressure changes due to friction are negligible.

Correctly defined boundary conditions. But, from a formal point of view, there is no information about the level of turbulence and also its spatial scale in the inlet cross-section. The SST turbulence model used, requires such data.

Fluid mesh independence analysis. Quite a narrow range of changes in the total number of elements, but changes in efficiency very small. It can be assumed that the test has been passed.

Mechanical parts.

In Fig. 4, one can see a dramatic change in grid density near the trailing edge or leading edge of the rotor blades. It does not seem necessary to make the mesh so dense in these areas. An abrupt change from a dense mesh to a sparse one is not a good idea.  But maybe I am wrong. Maybe the authors will explain the reasons that guided them.

Mesh sensitivity study is correct. But, it is not known what was the structure of the tested meches, where they were compacted. 

Line 149 "As it can be seen from the vortex intensity distribution in Figure 9, the vortex

characteristics before the outlet of the guide vanes are similar, which indicates that the

energy loss in these regions is mainly caused by wall laminar flow and has little relationship

with the guide vanes opening angle.” On what basis was this conclusion drawn?  The density of the grid shown in Fig. 2 does not allow for a detailed simulation of the flow in the wall layer. With such a high pumping height (545 m), friction losses are negligible.

The flow structure is disturbed and it is the reason for the losses, not friction on the walls.

The descriptions in Figure 11 are too small. They are difficult to read.

Line 168- "The dominant pressure fluctuation frequency of P4 is fn since the influence of RSI is weakened at the runner outlet." I think the sentence refers to the P5 point?

In the case of vibration of mechanical components, it is important to correctly adopt the position of the attachment points. It seems that the authors have adopted a sensible mounting arrangement.

Perhaps the 4fn frequency at P4 in Fig. 11 should be indicated? Other maxima are indicated.

It seems reasonable to relate the 4fn frequency in the flow to the 4fn frequency of mechanical vibrations.

Line 235 "The vortex generated at the bottom of the inlet side of the runner blades makes the low-frequency components of pressure fluctuation at 50% loading condition significantly increased." I don't see this vortex outside of Figure 9. In contrast, I see four major vortices in Figure 7b in the form of current line disturbances.

The authors try to explain the physical causes of the phenomena that occur, but I don't agree with some of the explanations.

The text is written clearly. Relevant information provided in an understandable and systematic way.

Overall, the article is interesting, written clearly. It should arouse the interest of readers.

I would only suggest increasing the readability of the drawings by enlarging them and enlarging the descriptions. I would drop the suggestion that friction has a significant effect on pressure distributions. I would revise some of the physical interpretations.

The paper, with minor revisions to the text and drawings, is suitable for publication.

Author Response

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Reviewer 5 Report

Dear Authors,

My opinion is positive about this paper.

The method is correct.

For mesh independence analysis the grid convergence index is more preferred. Figures 3 and 5 should be magnified in the relevant section.

I do not see any signs of boundary layer meshing, was any “inflation” applied in the fluid domain?

equation 7: pressure is lowercase and usually we divide the input dynamic pressure not with the static pressure, but since it is defined it can be accepted.

Please detail a bit more that hotspot in figure 9b.

 

 

I am missing the validation part. Please add it, validate your model.

Author Response

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Round 2

Reviewer 2 Report

The authors answered my comments and questions except comments 1 and 2. I repeat my questions again and would like to hear reasonable responses from them.
1.    In Fig. 3, the authors increased the mesh numbers from 2.4×106 to 3.6×106 (50% increment) but there is no sensible change in the efficiency. It seems the lower number of meshes should be tested to see the effect of mesh numbers on the results. Maybe a lower number of meshes is sufficient for this study.
2.    Why did the authors select efficiency for the mesh independence test?

Author Response

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Reviewer 3 Report

The have authors have replied the comments properly.

Author Response

We thank you for all the valuable suggestions and recommendations.

Reviewer 5 Report

Dear Authors,

I believe the recommended changes have been implemented successfully.

Author Response

We thank you for all the valuable suggestions and recommendations.