Numerical Simulation of Flow Field of Submerged Angular Cavitation Nozzle
Round 1
Reviewer 1 Report
Review of a manuscript titled “Numerical Simulation of Flow Field of Submerged Angular Cavitation Nozzle " by Dong et al. The authors have worked a very relevant problem of design of cavitating nozzle looking into effect of various geometric parameters. The presentation of literature review in this field of research is very good. But it lacks certain essential features of numerical work. It would recommend that authors take care of these aspects so that one can evaluate whether results obtained are good. Major Comments: 1. The abstract does not represent the work, state in the abstract what parameters are studied in the work for design of cavitation nozzle. 2. One of most important aspect of CFD modeling work to see whether the chosen model represent actual physical phenomenon. This done by comparing the numerical model with experimental results of similar nature. This is very essential. 3. The grid independence is also important ascertain that results presented is good. So, the authors have to show grid independence. In my opnion is grid is too coarse. 4. What is the first grid length normal to the wall? Was the y+ near wall less than 5. Only then enhanced wall function will be effective 5. The author should show the grid along the plane where the results are presented. 6. Section 2.4, is not presented properly, for example what do the author mean by “Import the written UDF to define it compressible” 7. In my opinion, the result in figure would be better if the authors resolve the grid using grid adaptation based on gradient of the volume fraction. 8. Why does effect of angle (alpha) in figure 10 is little absurd in the sense that vapor fraction is not varying with a trend. Why? Minor comments: 1. Sub title for section 3.1 is wrong. You have change it.
Author Response
The reviewer’s comment: The authors have worked a very relevant problem of design of cavitating nozzle looking into effect of various geometric parameters. The presentation of literature review in this field of research is very good. But it lacks certain essential features of numerical work. It would recommend that authors take care of these aspects so that one can evaluate whether results obtained are good.
Response: The authors are grateful to reviewer for his/her help. These comments are valuable and helpful for revising and improving our manuscript.
1 The reviewer’s comment: The abstract does not represent the work, state in the abstract what parameters are studied in the work for design of cavitation nozzle.
Response: Thanks for the comment. The authors have revised the abstract as suggested by the reviewers, where the parameters in the work for design of cavitation nozzle has been supplemented and quantified.
2 The reviewer’s comment: One of most important aspect of CFD modeling work to see whether the chosen model represent actual physical phenomenon. This done by comparing the numerical model with experimental results of similar nature. This is very essential.
Response: Thanks for the comment. In the revision, the authors have added a subsection (2.5 Validation of the simulation method) to the manuscript as the reviewer suggested. We conducted numerical simulation according to the experimental data in relevant literatures, and compared the simulation results with the experimental results to verify the correctness and feasibility of this model.
3 The reviewer’s comment: The grid independence is also important ascertain that results presented is good. So, the authors have to show grid independence. In my opnion is grid is too coarse.
Response: Thanks for the comment. Based on the reviewer's suggestion, we have added a paragraph and a figure (Figure 6) concerning the grid independence in the revised manuscript, after Figure 5.
4 The reviewer’s comment: What is the first grid length normal to the wall? Was the y+ near wall less than 5. Only then enhanced wall function will be effective.
The authors’ response: Thanks for the comment. In the revision, the explanation of y+ values has been added. Also, a figure (Figure 5) has been added. As can be seen, the value of y+ is within a reasonable range, so the height of the grid in the first layer can be considered justified.
5 The reviewer’s comment: The author should show the grid along the plane where the results are presented.
The authors’ response: Thanks for the comment. Based on the reviewer's suggestion, we have added the meshing images in the revised manuscript, as shown as the added Figure 7.
6 The reviewer’s comment: Section 2.4, is not presented properly, for example what do the author mean by “Import the written UDF to define it compressible”.
The authors’ response: Thanks for the comment. We think that it is necessary to reflect the influence of fluid compressibility on cavitation. In the original manuscript, the expression function provided by CFX is adopted. In the revision, the statement “Import the written UDF to define it compressible” has been revised as “The physical properties of the fluid are shown in Table 1. User defined density function (UDF) of water vapor to achieve mixture compressibility.” Accordingly, Table 1 has been added.
7 The reviewer’s comment: In my opinion, the result in figure would be better if the authors resolve the grid using grid adaptation based on gradient of the volume fraction.
The authors’ response: Thanks for the comment. The grid adaptation based on gradient of the volume fraction indeed is a great method of mesh. However, it is difficult to implement this grid adaptive technology in CFX software. This technology will be studied in our future work. In Conclusion, it has been mentioned at the end of the section.
8 The reviewer’s comment: Why does effect of angle (alpha) in figure 10 is little absurd in the ense that vapor fraction is not varying with a trend. Why?
The authors’ response: Thanks for the comment. As the reviewer said, the vapor fraction corresponding to different α shows roughly the same trend. It is because the angle of contraction section (α) has less effect on the cavitation [25]. The change of the α will affect the bunching of the jet. On one hand, it will cause the energy loss and thus affect the jet velocity. On the other hand, it will affect the flow state of the jet and hence affect the cavitation. However, the main cavitation region of the angular cavitation nozzle is located in the expansion section. In the revision, the explanation has been added, before Figure 14.
[25] Yang Y, Li W, Shi W, et al. Numerical investigation of a high-pressure submerged jet using a cavitation model considering effects of shear stress [J]. Processes, 2019, 7(8): 541.
9 The reviewer’s comment: Sub title for section 3.1 is wrong. You have change it.
The authors’ response: The authors thank the reviewer for pointing out this mistake. We have modified the title as “3.1. Preliminary analysis of nozzle flow field”.
Reviewer 2 Report
The manuscript aims to investigate computational results in terms of the flow field of submerged cavitation nozzles. It is interesting and falls within the scope of the journal. However, the manuscript in its present form has several weaknesses. The following should be adequately revised to justify a recommendation for publication.
1. The abstract needs to be changed and revised to be more quantitative. You can attract readers' attention by listing some numerical results in this section.
2. Line 11: Pleased give the full name of the turbulence model (Renormalization group (RNG))
3. The main objectives of this study and the novelty point should be discussed clearly and in detail. Make the novelty clearer and in the context of existing literature.
4. Which gap in the literature does this study intend to fill, and what contribution does it make to the literature? Please highlight more in the introduction section.
5. Why did you choose the RNG k- É› turbulence model? Please justify. Some researchers suggest the RNG k- É› turbulence model because of its high accuracy (https://doi.org/10.1016/j.biosystemseng.2019.04.009; https://doi.org/10.1016/j.biosystemseng.2007.02.009; https://doi.org/10.17660/ActaHortic.2005.691.55)
6. Please cite Lines 181 and 213.
7. Lines 232-242: How did you find the optimum mesh number? Did you perform a mesh-sensitive test?
8. You can summarize the initial boundary conditions in a Table.
9. Please change the title of Figures 4-6. Please express them in a different way.
10. Have you compared the numerical results with experimental data? Without experimental data, we cannot say with certainty whether the model is accurate or not.
11. The results and discussion section should explain differences or similarities with the results of previous studies.
12. Limitations are not included in the present form.
13. Future directions are not clearly indicated.
14. The conclusion should address the highlights of this paper and, at the same time, give new directions for further studies.
15. Please check all parts of the manuscript and correct grammatical errors.
Author Response
The reviewer’s comment: The manuscript aims to investigate computational results in terms of the flow field of submerged cavitation nozzles. It is interesting and falls within the scope of the journal. However, the manuscript in its present form has several weaknesses. The following should be adequately revised to justify a recommendation for publication.
The authors’ response: The authors are grateful to reviewer for his/her help. These comments are valuable and helpful for revising and improving our manuscript.
1 The reviewer’s comment: The abstract needs to be changed and revised to be more quantitative. You can attract readers' attention by listing some numerical results in this section.
The authors’ response: Thanks for the comment. The authors have revised the abstract to the manuscript as suggested by the reviewers, where some numerical results have been added.
2 The reviewer’s comment: Line 11: Pleased give the full name of the turbulence model (Renormalization group (RNG)).
The authors’ response: Thanks for the comment. In the revision, the full name of the turbulence model (Renormalization group (RNG)) has been given.
3 The reviewer’s comment: The main objectives of this study and the novelty point should be discussed clearly and in detail. Make the novelty clearer and in the context of existing literature.
The authors’ response: Thanks for the comment. The authors have added some sentences in the last paragraph of introduction to make the objective and novelty of the paper clearer.
4 The reviewer’s comment: Which gap in the literature does this study intend to fill, and what contribution does it make to the literature? Please highlight more in the introduction section.
The authors’ response: Thanks for the comment. The authors have added a paragraph to explain the gap in the literature. In the following paragraph, the contribution of the paper is highlighted further.
5 The reviewer’s comment: Why did you choose the RNG k-É› turbulence model? Please justify. Some researchers suggest the RNG k-É› turbulence model because of its high accuracy (https://doi.org/10.1016/j.biosystemseng.2019.04.009;https://doi.org/10.1016/j.biosystemseng.2007.02.009; https://doi.org/10.17660/ActaHortic.2005.691.55 )
The authors’ response: Thanks for the comment. In the revised manuscript, the several paragraphs concerning the selection of this turbulence model have been added, right after the title of subsection 2.2.3 Turbulence Model. Also, the important reference mentioned by the reviewer has been added in the revision, as given as Ref.[28].
6 The reviewer’s comment: Please cite Lines 181 and 213
The authors’ response: Thanks for the suggestion. According to the reviewer's suggestion, the authors have added the citations in the corresponding places. The specific modifications are as follow.
Line 181(in original manuscript, Line 194 in revision): The model uses the Rayleigh-Plesset equation for the description of bubble growth and collapse [26]
Line 213 (in original manuscript, Line 253 in revision): For the standard - model cannot accurately predict the impact of transient flow and bending streamline, the - model can reduce the calculation error to a certain extent and expand its field of application by modifying the turbulent dynamic viscosity coefficient [24].
7 The reviewer’s comment: Lines 232-242: How did you find the optimum mesh number? Did you perform a mesh-sensitive test?
The authors’ response: Thanks for the comment. In the revision, we have added a paragraph and a figure (Figure 6) concerning the grid independence, after Figure 5.
8 The reviewer’s comment: You can summarize the initial boundary conditions in a Table.
The authors’ response: Thanks for the comment. In the revision, we have added a table (Table 2) in section 2.4 to represent the initial boundary conditions for the numerical simulation.
9 The reviewer’s comment: Please change the title of Figures 4-6. Please express them in a different way.
The authors’ response: Thanks for the suggestion. In revision, Figures 4-6 have been renumbered as Figures 10-12. Their titles have been changed.
10 The reviewer’s comment: Have you compared the numerical results with experimental data? Without experimental data, we cannot say with certainty whether the model is accurate or not.
The authors’ response: Thanks for the comment. In the revision, the authors have added a subsection (2.5 Validation of the simulation method) as the reviewer suggested. We conducted numerical simulation according to the experimental data in relevant literatures, and compared the simulation results with the experimental results to verify the correctness and feasibility of this model.
11 The reviewer’s comment: The results and discussion section should explain differences or similarities with the results of previous studies.
The authors’ response: Thanks for the comment. In the revision, differences or similarities with the results of previous studies have been added, which can be found at the paragraph before Figure 13, the last paragraph of 3.1 section, the first paragraph of 3.2 section, and the last paragraph of 3.3 section. All supplements have been highlighted.
12 The reviewer’s comment: Limitations are not included in the present form.
The authors’ response: Thanks for the comment. The authors think that the main limitation is the lack of experiment verification of the optimized angular cavitation nozzle. In the revision, we add a paragraph concerning the limitation, at the end of the conclusion section.
13 The reviewer’s comment: Future directions are not clearly indicated.
The authors’ response: Thanks for the comment. Based on the reviewer's suggestion, at the end of the conclusion section, we have added a paragraph to indicated the future work, which concerns the experiment verification and the study on grid adaptation technique.
14 The reviewer’s comment: The conclusion should address the highlights of this paper and, at the same time, give new directions for further studies.
The authors’ response: Thanks for the comment. As suggested by the reviewer, in the revision we add a statement on the highlights of the paper, in the first paragraph of conclusion section. Meanwhile, in the last paragraph of this section, we state the directions of future study.
15 The reviewer’s comment: Please check all parts of the manuscript and correct grammatical errors.
The authors’ response: Thanks for the comment. In revising the manuscript, we try our best to correct grammatical errors and typos. All corrections have been highlighted.
Reviewer 3 Report
This paper discusses the numerical simulation of the flow field of submerged cavitation nozzle. In this context, multiphase mixture model, cavitation model and RNG k-ε turbulence model are applied. The authors investigate the effects of the inlet contraction part, parallel middle part and outlet expansion part on the velocity and vapor volume fraction.
However, I think the manuscript is an incomplete state and too short. I can't find the main purpose and originality in the current manuscript. My recommendation is that it should be rejected; at the same time, I encourage the authors to extend the scope of their work and improve new findings and related technical discussions:
- The English has to be improved.
- Numerical results should be given in abstract section.
- Authors show well known facts only.
- The paper is a very simple technical work without any impact to science.
- There are lots of studies related with cavitation nozzle as you refer in the introduction section. What is the novelty of this work? These details must be given at the last paragraph of introduction section.
- The main purpose of the study was not given. It is stated that different topics will be investigated, but what is the main purpose? These details must be given at the last paragraph of introduction section.
- Subheadings are given quite irregularly as shown in below.
2.1. Physical model of angular cavitation nozzle
2.2. Physical model of angular cavitation nozzle
1. Multiphase flow mixture model;
2. Cavitation Model;
3. Turbulence Model
2.3. Meshing
2.4. Boundary Condition
It needs to be planned better. For example:
2.1. Geometry,
2.2. Physical models
2.2.1. Multiphase flow mixture model
2.2.2. . Cavitation Model
2.2.3. Turbulence Model
2.3. Meshing
2.4. Boundary conditions
- In the meshing section, there is no grid independency test. It is great lack, especially in studies with only numerical results.
- The results and discussion part is lack of scientific aspects and the results section must be improved with scientific aspects.
- The results of this study must be comparised with the studies in literature. It is very important.
- In the results and discussion section, it is said that “3.1. Boundary condition”. However, it would not be correct to give it as a result of boundary conditions. In this section only the results of “α = 13.5°, Ld = 3d, Le = 4d, 258 β = 60°” were given as an example. However, it is not fully explained why this is done.
These comments can be seen also in attached file.
Comments for author File: 
Comments.pdf
Author Response
The reviewer’s comment: This paper discusses the numerical simulation of the flow field of submerged cavitation nozzle. In this context, multiphase mixture model, cavitation model and RNG k-ε turbulence model are applied. The authors investigate the effects of the inlet contraction part, parallel middle part and outlet expansion part on the velocity and vapor volume fraction.
However, I think the manuscript is an incomplete state and too short. I can't find the main purpose and originality in the current manuscript. My recommendation is that it should be rejected; at the same time, I encourage the authors to extend the scope of their work and improve new findings and related technical discussions:
The authors’ response: The authors are grateful to reviewer for his/her help. These comments are valuable and helpful for revising and improving our manuscript. According to the reviewers’ comments, we revised the manuscript carefully and added some contents on literature review, turbulence model, grid independence check, y+ values, boundary condition, validation of the simulation, limitation and future work.
1 The reviewer’s comment: The English has to be improved.
The authors’ response: Thanks for the comment. In revising the manuscript, we try our best to correct grammatical errors and typos. All corrections have been highlighted.
2 The reviewer’s comment: Numerical results should be given in abstract section.
The authors’ response: Thanks for the comment. The authors have revised the abstract as suggested by the reviewers, where some numerical results have been added.
3 The reviewer’s comment: Authors show well known facts only.
The authors’ response: Thanks for the comment. In the revision, differences or similarities with the results of previous studies have been added, which can be found at the paragraph before Figure 13, the last paragraph of 3.1 section, the first paragraph of 3.2 section, and the last paragraph of 3.3 section. All supplements have been highlighted.
4 The reviewer’s comment: The paper is a very simple technical work without any impact to science.
The authors’ response: Thanks for the comment.
5 The reviewer’s comment: There are lots of studies related with cavitation nozzle as you refer in the introduction section. What is the novelty of this work? These details must be given at the last paragraph of introduction section.
The authors’ response: Thanks for the comment. In the revision, the novelty of the paper has been explained in more details, at the last paragraph of introduction section. As stated, although the existing literature has discussed the jet and cavitation characteristics of the cavitation nozzle under submerged and non-submerged conditions, the focus is mostly on the accuracy of the model, and the optimized of nozzle structure has no practical application. In this paper, we have designed and optimized a cavitation nozzle for underwater creature removal, and establishes the three-dimensional (3D) physical model of the angular cavitation nozzle in the submerged state by using CFX fluid simulation soft-ware.
6 The reviewer’s comment: The main purpose of the study was not given. It is stated that different topics will be investigated, but what is the main purpose? These details must be given at the last paragraph of introduction section.
The authors’ response: Thanks for the comment. The main purpose of the study is to optimize the structure of cavitation nozzle by using CFD technique. In the revision, this statement has been added to the last paragraph of introduction section.
7 The reviewer’s comment: Subheadings are given quite irregularly as shown in below.
2.1. Physical model of angular cavitation nozzle
2.2. Physical model of angular cavitation nozzle
- Multiphase flow mixture model;
- Cavitation Model;
- Turbulence Model
2.3. Meshing
2.4. Boundary Condition
It needs to be planned better. For example:
2.1. Geometry,
2.2. Physical models
2.2.1. Multiphase flow mixture model
2.2.2. Cavitation Model
2.2.3. Turbulence Model
2.3. Meshing
2.4. Boundary conditions
The authors’ response: Thanks for the suggestion. In the revision, subheadings have been rewritten as,
2.1. Physical model of angular cavitation nozzle
2.2. Mathematical model of angular cavitation nozzle
2.2.1. Multiphase flow mixture model
2.2.2. Cavitation Model
2.2.3. Turbulence Model
2.3. Meshing
2.4. Boundary conditions
2.5. Validation of the simulation method
8 The reviewer’s comment: In the meshing section, there is no grid independency test. It is great lack, especially in studies with only numerical results.
The authors’ response: Thanks for the comment. Based on the reviewer's suggestion, we have added a paragraph and a figure (Figure 6) concerning the grid independence in the revised manuscript, after Figure 5.
9 The reviewer’s comment: The results and discussion part is lack of scientific aspects and the results section must be improved with scientific aspects.
The authors’ response: Thanks for the comment. We reedited the part of result and discussion to make it as scientific as possible. We reduce some visual statements on the figures, explain the conclusions shown in the figures concisely instead. Moreover, we compare our work with existing studies.
10 The reviewer’s comment: The results of this study must be comparised with the studies in literature. It is very important.
The authors’ response: Thanks for the comment. In the revision, we added some studies in literature to be compared, in the result and discussion section.
11 The reviewer’s comment: In the results and discussion section, it is said that “3.1. Boundary condition”. However, it would not be correct to give it as a result of boundary conditions. In this section only the results of “α = 13.5°, Ld = 3d, Le = 4d, 258 β = 60°” were given as an example. However, it is not fully explained why this is done.
The authors’ response: Thanks for the comment. In the revision, the author modified the title of 3.1 section to make it more relevant to the content. The reason why only the results of “α = 13.5°, Ld = 3d, Le = 4d, 258 β = 60°” were given as an example is that this part is a preliminary analysis of the cavitation jet flow field, which makes preparation for the study of the effect of the structural parameters of cavitation nozzle on cavitation. In order to make a better presentation of the internal and external fields of the cavitation jet, the finally optimized structural parameters of the nozzle were selected as an example for analysis. In the revision, we have added a statement to clarify the selection of parameters.
Round 2
Reviewer 1 Report
The authors have tried their best to address the queries raised. I am not still fully convinced with the validation case presented. But, the nature of the work and presentation is okay. Due to this reason, I am going to accept the paper as a border case.
Reviewer 2 Report
The authors have greatly improved the article according to the suggestions. The article is currently acceptable
Reviewer 3 Report
· Authors suggestions and critique of the reviews very carefully studied.
· The authors review the work very seriously.
· Weaknesses have been completed.
· These corrections and additions seem enough.
· The study complies with the acceptance state.
