Effect of the Diameter of Pressure-Balance Pipe on Axial Hydraulic Thrust
Round 1
Reviewer 1 Report
The authors revised the manuscript in accordance with my suggestions.
For this reason I propose the publication of this paper.
Author Response
Dear reviewer,
Thanks for your suggestion, I will continue to make progress in my work .
Reviewer 2 Report
I am happy about the revised version of the paper.
In my opinion now it can be accepted. However, maybe the Authors could give a look at [A1] to improve the literature review.
[A1] Martins, N.M.C., Brunone, B., Meniconi, S., Ramos, H.M., and Covas, D.I.C. (2017). CFD and 1D approaches for the unsteady friction analysis of low Reynolds number turbulent flows. J. of Hydraulic Engineering, ASCE, 143(12), 04017050.
Author Response
Dear reviewers,
Thank you very much for your comments.
I have read the literature recommended by you. This paper mainly adopts the one-dimensional calculation method, which is very meaningful. It is related to my work in this paper, but also has some gaps.
I will also further improve my work.
Reviewer 3 Report
BRIEF SUMMARY
The paper presents the study of the effects of the variation of the diameter of pressure-balance pipe in axial hydraulic thrust in a pump turbine.
The manuscript has a length of 16 single-spaced one-column pages including 13 figures, 5 equations and 6 tables. However, the format of the paper is in the "Track Changes" function in
Microsoft Word. To the reviewer understanding, the paper could accomplish the instructions and standards of the journal in this matter. But please, check it.
The reviewer believes that the work presented is an approach to the improvement of the axial thrust characteristics of a pump turbine, and it could help to understand its design and it will assistance in future units specially regarding to the studied effects and performance parameters. Nevertheless, several aspects of the manuscript could be improved or better addressed, and they are commented as follows.
BROAD COMMENTS
The reviewer thinks the abstract in the current version needs to clarify and point out the cause of the axial trust reduction at 50% load condition. A sentence at the end with the major conclusion would be useful.
The reviewer finds the State of Art could be improved by clearly presenting the conclusions from the review of existing studies. The reviewer believes this introduction section includes specific State of Art in order to place authors’ work and select, comment and refer the most significant ones to ensure that the authors are aware of similar research work performed by other researchers. For instance, reference [15] is authors' own work and consequently, the authors should point out the new contribution in this manuscript.
The function of the pressure-balance pipe has to be better shown. It is necessary to give a better explanation of how it works, the difficulties of this technology, etc.
SPECIFIC COMMENTS
Page 2 Line 64 reads: "The use of the pressure-balance pipe will cause a certain volume loss of the pump-turbine and reduce the efficiency of the pump-turbine." But the use of pressure-balance pipes if to reduce the shaft axial hydraulic thrust, authors' claim, to be more efficient and reduce load and friction loss. This reviewer finds contradictory these statements. Please, revise them.
Page 2 Line 79 and Line 84 start with "However ..." and they are almost the same sentence.
Sincerely, Figure 1 is quite difficult too understand. It should be a zoom part of a whole turbine in order to gain in comprehension. The three parts of the simulation have to be name-labelled in the figure.
Table 1 and label of models (D, D-100 and D+100) should be shown in Figure 3 to gain in comprehension.
*** CFD work ***
Is this work performed by using a commercial CFD software? If it is so, a licence is necessary to work with it. There is no evidence of the existence of the appropriate licence to publish this work. Then, I strongly suggest confirming this aspect. Moreover, in the References section there is no evidence of the user guide and/or manual used.
What does it mean "... and the grid quality is was greater than 0.32."
In addition, the authors really should accomplish these minimum best practice rules using numerical results from CFD simulation, specifically for section 4 of the paper:
- To describe the numerical method used. It is not enough to state, for example, that the method is based on a “conservative finite-volume formulation” giving then a reference to a general CFD textbook.
- Mesh type, elements type, etc.
- Mesh quality: mesh convergence and independence, cell skewness criterion for a good mesh quality, etc. (Only this sentence in the paper is not acceptable: "After comprehensively considering grid quality, accuracy and computing resources, a grid independence verification, the was conducted, then a grid unit number of about 8 million ...")
- Boundary conditions have to be not just presented but justified
- The limitations of the algorithm that become clear from the results should also be indicated. It is necessary to comment on when this algorithm can be applied and under what conditions.
Another CFD Questions: Why the turbulence model used in this paper is k-omega SST model? A justification has to be provided. What about the y+? Are wall functions used?
IMPORTANT: since authors explain the importance of cavitation, is there any cavitation model implemented in this calculation?
Figure 5 shows torque and efficiency. How does this efficiency calculated? It is necessary to show and explain.
How are forces F1 and F3 calculated, for instance? It is necessary again to show how is calculated.
IMPORTANT: The section 6 is too descriptive. The results are presented in the figures and these figures are described in the text. However, a discussion of the results is necessary. The discussion is an opportunity for authors to explain what their findings mean, to illuminate the key conclusions, and to address potential criticism.
OTHER COMMENTS
- Page 12, spelling mistake with "FIGURE 10. _It ..."
- Table 3 shows units of [N·m] in capital letters. The rpm has a precision of two decimals. How is this precision obtained in experimental work?
- Figure 4 does not provide much information.
- Figure 5 should be presented all three loads in just one graphic. The same applies to Figures 8, 9 and 10.
- Why are the three points of results of the simulation connected with a continuous line?
- In Table 3 experimental results are presented but only introduced with a reference. Then, this reviewer strongly encourages adding this information regarding the experimental results without the necessity to go to the reference. It would help to understand the comparison.
- In section 3 the pressure-balance pipes (3 models - Figure 4) and the distribution are presented. How were these diameters decided? Based on a Design of Experiments (DoE)? Own experience? Please comment it.
QUESTIONS
Other issues and questions to note are:
*** Under what conditions do the authors consider that the model will not be adequate? Under what conditions will require additional research for the reliability of the results?
*** The limitations of the methodology that become clear from the results should also be indicated.
*** The conclusion section is too general, too scarce. It is necessary to be more in detail, to emphasize the conclusion of the results. Definitely, the findings and conclusions are not stringent and comprehensible as should be.
*** How can research in the field be continued? There is no future work description.
OVERALL RECOMMENDATION
In general, in the opinion of the reviewer, this paper can bring insights to the field. The reviewer thinks that the topic is of interest and will provide useful information to those who are in the same design field as the authors.
The paper could gain in quality and comprehension, especially in the CFD explanation. An improvement can be done to fully understand and have a general idea of the work, the results and conclusions. The current composition, edition and format of the manuscript are more presented as a technical review than a research paper.
A weak point of the work is the CFD study, owing to the vague description and detailed explanation. The CFD study is the goal of the work and then must clearly be show its characteristics. Results from CFD are not shown. The mesh is not shown. For instance, pressure distribution map fields, streamlines, relative velocities, etc. are not presented and discuss.
The authors' reference to their own work in the reference [15], a paper also published this year 2021 in the JMSE journal. By revising it, this reviewer totally encourage the authors to follow the same structure, layout, presentation, graphics, diagrams and completeness in this current manuscript. In addition, it is necessary to clearly point out the new contribution of this paper.
Hence, the paper could be acceptable for publication with major revision needed.
Author Response
see the attachment
Author Response File: 
Author Response.docx
Round 2
Reviewer 3 Report
Thanks to the authors for your responses. The paper has gained in value and several parts of it have been improved. The authors have answered some of the reviewer’s comments, but not all of them. Then, this reviewer could differ in several responses, such as:
- For instance, reviewer's question: " - Figure 4 does not provide much information. " -> Authors' response: " The position has been adjusted. ". However, Figure 4 is exactly the same in the previous and this current manuscript, no change at all, exactly the same.
- New formula (6) to (8) show n_11, Q_11, M_11 and H definitions and Table 4 the units are (rpm), (m3/s), (N·m) and (m). But, are the units of these equations correct? For instance, in (6), are not the units of n_11 = (rpm·m^0.5), or in (7), Q_11 = (m^0.5/s). I think it is important to check it.
- The authors' reference to their own work in the reference [15], a paper also published this year 2021 in the JMSE journal. As I commented in my review, I totally encouraged the authors to follow the same structure, layout, presentation, graphics, diagrams and completeness in this manuscript and the necessity to clearly point out the new contribution here. This question has not been answered.
- This reviewer has not change the opinion of the CFD study. As I commented in my review, the CFD approach should be used to a better design in the most conflictive parts of the pressure-balance pipe. The CFD description is vague and poor in detailed explanation. The CFD study is the goal of the work and then must clearly be show its characteristics. The mesh is not shown. Results from CFD are not shown: pressure distribution map fields, streamlines, relative velocities, etc. are not presented and discuss.
- I believe this manuscript needs a nomenclature section.
- This reviewer could not find evidences in the manuscript of the existence of the appropriate licence of the commercial software to publish this work.
- The revised parts are marked in red in the paper. Honestly, not much "marked in red" can be seen in the new version of the manuscript, around 15 sentences.
Finally, I believe this paper could be improved. I believe it would result in a more understandable and valuable version of the paper attending this reviewer's comments.
Author Response
See the attachment.
Author Response File: Author Response.docx
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
The paper focuses on the analysis of the influence of the variation in the diameter of the passage pipe on the axial thrust of the water in order to avoid the excessive load of bearing and frame, and to ensure the safety and stability of the pump turbines. The authors studied the variation of the axial hydraulic thrust caused by the variation of the pipe diameter of the equalization pipe below 100%, 75% and 50% of the load of a pump turbine.
Even if the results are not very original and this problem has already been addressed in the current literature, the work is well organized and in any case could represent a guideline for the sizing of pumping turbines. Perhaps the authors should emphasize in the abstract that their study was approached with numerical simulations in CFD.
Minor revisions:
There is some typo in the text and uppercase letters are often used instead of lowercase letters.
Revising the text of the references is also inconsistent with the Journal's guideline.
Authors should better specify what they represent in the Figures and Tables (where data and results are present) by improving their caption.
Also, I guess that a list of symbols used at the bottom of the manuscript might be useful.
Reviewer 2 Report
In my opinion this paper cannot be accepted for publication since there is a strong need of corroborating the numerical results with experimental ones.
