Evolution Characteristics of Suction-Side-Perpendicular Cavitating Vortex in Axial Flow Pump under Low Flow Condition
Round 1
Reviewer 1 Report
Authors analysed the development of suction-side-perpendicular cavitating vortex in axial flow pump. Some comments to improve the manuscript as it need revision:
- Revise English (lines 28-29, three times cavitation).
- Reference 4 should have date.
- Revise description of references. The same author is cited differently.
- Only Surname should be cited in line 41, 5.
- Typing errors occur.
- Revise the last paragraph of Introduction and clearly determine the aim of the paper, what is its novelty and later the used methods.
- Line 71: Figure No should be written. Figures 1 and 2 must be mentioned in the text of the manuscript. Add what is presented in Figure 2.
- What is the accuracy of the measurements? Explain how the measurements were performed.
- The description of the model should be more detailed.
- Explain all quantities in Eq. 3.
- Figure 7 is not mentioned in the text. What is the reason of difference between simulation and the experiment?
- Authors should arrange the markups in the text.
- The general equations must be transferred to the methodology, not to the results.
- What is in lines 330-344?
- Explain the Family force as it is mentioned only in 309 line and in Conclusions.
- Revise conclusions and their structure.
- What are some quantitative results? They should be added into conclusions.
- What are limitations of the study?
- Authors need to review formatting rules as the paper looks like not finished.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
The paper reports results obtained from the analysis of numerical data related to the evolution characteristics of suction-side-perpendicular cavitating vortex in axial flow pump. Generally speaking, the paper is well presented and rather well written and the results are innovative so that I consider that the paper should deserve publication after revision.
First of all, some parts of the paper need to be rewritten because they are written so badly that I could not understand their meaning. This is for instance the case for several sentences in the abstract (line 14, lines 18-21), in the introduction (lines 43-45, lines 55-60), line 232 ("Due to the complex conditions, both cavitation and vortex produce velocity gradient" : what is supporting this claim, in a precise and quantitative way ?), line 261 ("the cloud cavitation shedding at the tail of the blade affects each other with the formation of the vortex": what does this mean ?). Also, what does the "family force" mean exactly (this term is used several times) ?
Then, I think that several points should be explained and validated in a more detailed way. For instance, line 152, it is claimed that "when the cavitation number is 0.18, the vertical cavitation vortex is relatively stable and develops for a long time ..." : how can we infer this from the results presented in figure 7 ? In figures 8 and 9, how are the reported trends obtained in a precise way ? In fig. 8, this concerns the so-called cavitation patterns and in fig. 9 this concerns the so-called vapour volume fraction. How are both obtained ? This must be explained and described in a very precise way. In addition, how do the fluid local properties (density, viscosity) vary when vapour appears ? How do the values of the parameters described in relations 1 and 2 influence the results (i.e. evaporation coefficient, condensation coefficient, and so on ...) ?
Finally, lines 330-344 should be removed from the text.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
Review of the paper “Evolution characteristics of suction-side-perpendicular cavitating vortex in axial flow pump under low flow condition” proposed for publication in Journal of Marine Science and Engineering by Lin Wang et al.
The paper proposes a detailed analysis of the flow in an axial flow pump operating at one partial flow rate in cavitating conditions. The analysis mostly uses the results of numerical simulation.
- The section “introduction” proposes an overview of scientific literature regarding the analysis of low in cavitating axial flow pumps. From the reviewer’s point of view that review is too much limited to references (some in Chinese) coming from China. A lot of publications on the subject have also been proposed from a long time ago by US, European, and Japanese researchers: a selective analysis of the main methods and results used in these references should be done. As an example, many papers can be found regarding cavitation in inducers for spatial applications.
- Section 2:
- Regarding the test rig and methods, the authors do not give any information about the quality of experimental results (uncertainties on head, flow rate, efficiency) which is of course necessary to appreciate the quality of numerical simulations.
- The experimental curves of head and efficiency versus flow rate should be given, as well as the specific speed (or type number) of the tested pump, and a value of one Reynolds number.
- As the presentation concerns a specific flow rate (70% of best efficiency conditions) it is necessary to add some more comments regarding the choice of that flow rate (comparison with impeller critical flow rates for inlet and outlet recirculation, instability or not observed in the characteristics curves, …)
- Regarding the grid, can the authors add data about the grid within the gap between impeller and casing, and values of Y+ in that zone
- In sub-section 2.2.2, the models (turbulence model, cavitation model) that have been used are not really discussed: what could be some other choices and why (based on literature survey) the choices are the best (or not). For example, as the partial flow rates are of interest, can the use of DES be a better solution as described by other authors for other types of machines; Is Zwart model the better solution to describe unsteady cavitation?
- Sub-section 2.2.3: how is the steady solution obtained?
- Sub-section 2.2.4: what is the value of the flow rate used for the analysis of mesh independence? What is the type of model (steady, unsteady) used to establish figure 6?
- Figure 7: uncertainties of experimental data should be given as well as uncertainty evaluation of numerical procedure
- Sub-section 3.1.1:
That paragraph is very important as it describes using results coming from experiments (especially high-speed camera) and from numerical model. The results are well presented, even if some questions remain:
- Is there a periodicity of the phenomenon that is described (with a period different from impeller rotation or blade passing frequency)? If yes, what is the frequency?
- What can be said regarding the evolution of the instantaneous flow rate in each blade passage?
- Is there an analogy of the cavitation patterns with what has been described a long time ago and called rotating stall (see for example axial compressors)?
- What can be the influence of the gap between blades and casing on the development of what is described?
- Presentation of numerical results
Various tools are proposed and applied to the specific test case: turbulent kinetic energy, Liutex method for identification of vortices, vortex velocity gradient, vortex kinetic energy, vorticity analysis in impeller. This is of course interesting. Nevertheless the comparison between these methods (interest, advantages, …..) is not really proposed. So, for a non-specialist it remains difficult to appreciate what can be useful for a new study. The reviewer would be more satisfied if such a comparison was made.
- Conclusion
In the conclusion, it is quite impossible to understand what are the main originalities of the work. That must be done more explicitly. Some perspectives should also be added.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Authors made revision and a lot of improvements were done. However, the manuscript still needs some improvements and can’t be published in current state:
As a reviewer, I would strongly recommend using the Nomenclature, as still exist some nonations and quantities not described, e.g. Eq. 11 and 12: it is not clear what is m? It is mass flow rate or just mass? In addition revise other equations: µkf, etc.
Revise English.
What was gas density in Eq, 12?
Seconds should be s not S (see line 234). In addition, Qd must be explained.
What value is taken for water density (line 271).
Title of the Figure should start from capital letter.
Some equations should presented not in the results section but in Methodology, e.g. calculation of the kinetic energy (eq. 19). In addition, only w is explained, add v and u.
Still typing errors occur.
Author Response
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Author Response File: Author Response.pdf
Reviewer 2 Report
I have now read the revised versioon of the paper. It has been significantly improved. However, a few points still need to be considered for minor revision.
For instance, in the abstract, what does this mean ? Please make corrections : "The vorticity is the main contribution of the vorticity in the vortex stretching term and the vortex expansion term. The vorticity is mainly caused by the deformation of the fluid particles in the process of vortex development."
The reference "cav2003" must be corrected in the introduction. Also correct "vortexticity" in the introduction. Write "vortices" and not "vortexes" everywhere "vortexes" is used.
Write numbers in a correct and meaningful way everywhere this is required. For instance, line 237 where "0.3310344s" is used, or line 238 where "0.0003448275s" is used.
What is the meaning of the sentence "The damage stage affects only a small range of vortex kinetic energy near the blade" (line 465 ) ?
Change "In order to study the causes of vorticity" to "In order to study the origins of vorticity" (line 493 and everywhere this is used).
What does the sentence "More abstract understanding is more difficult than other methods" (line 603) mean ? Please rewrite this sentence.
Similarly, rewrite lines 598-601 ("The vortex kinetic energy shows the influence of the vortex from the perspective of energy. Especially in the pump, the energy of the vortex comes from the mechanical energy of the impeller rotation. The greater the energy of the vortex is, the lower the inevitable efficiency is, and the influence degree of the vortex can be judged").
Author Response
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Reviewer 3 Report
The quality of the revised paper is much better. Many responses have been made with reference to the reviewer’s observations. Regarding the content, it seems now possible to publish it. The reviewer has only two questions that should be answered or corrected before publication:
- In various parts of the text, the authors say that they are studying “evolution of vertical cavitation vortex at low latitude”; the use of “vertical” and “altitude” should be at least explained or perhaps corrected
- The reviewer recommends that the authors read seriously the new paper they propose especially regarding the English spelling.
Author Response
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Author Response File: Author Response.pdf
