Three-Dimensional Numerical Simulation of Flow Structure in Annular Flume Based on CFD Study of Water

Round 1

Reviewer 1 Report

This manuscript focused on the water flow structure of the annular flume under different rotational speed ratios. The studied model is a prototype of the annular flume at Hohai University. The axial flow velocity and vortices in the flume as the function of rotational speed ratio was studied.

However, I do not recommend the publication in the journal Water.

Some of my concerns:

1.       First, the research background is unclear. The particle (sand) sedimentation in such annular flume is engineering background. It was mentioned the tracer sand motion is very important. The authors reviewed the 3D flow in introduction part. However, the flow structure and related problem is unclear. The motivation is not clearly presented. It seems a simplified CFD model on the annular flume at some other labs. Later on the authors described water-gas two-phase flow in the annular flume and VOF model in section 2.3. What’s the logic behind this? VOF model is suitable to study the flow water-air interfacial problem not the particle motion problem. What’s the main problem or motivation of this study?!

2.       In general, 3D simulation is not a new topic, it is very common after year 2000. The single phase flow in such simulation is very common after 2010. The VOF or similar methods were used to simulate the two-phase flow in earlier 2005 to 2010. The authors stated that the VOF method is complex and time-consuming to calculate. I personally do not agree. This is difficult before year 2005. As a pity, this research utilized a 3D single phase flow method to study the flow in the annular flume. The authors emphasized the focus is the axial flow velocity and secondary flow etc. However, the descriptions on the model and engineering application is not clear. What’s the research status of secondary flow?

3.       The model details are missing. Where is the rotation part? Could it be water at room temperature? The modeling fluid details could be given.

4.       For turbulence model, RNG is OK. Please double check the presentations of the models.

4.1    To name a few, In equation 2 to 4, make sure the subscript 1,2,3 in velocity u is standard type in the LHS (Left Hand Side)  of equations (u₁) or italic type in the RHS (Right Hand Side) of equations (u₁ or u₁). Later in line 142, what is vr? Why not use velocity u?

4.2    In equation 5, the first term in RHS of equation should be derivative of turbulent energy K not e.

4.3    Line 111, maybe turbulent viscosity not velocity.

4.4    In equation 7, make sure turbulent energy is k or K. Also equation 7 appears in line 113 one more time.

4.5    Use standard k-ε to replace the descriptions of SKE

4.6    RNG k-ε turbulent flow model, turbulent model not Turbulent flow model.

5.       Some other details on CFD, please use professional descriptions. Please!

5.1    To name a few, Grid Independence study not irrelevance in tittle section 2.4

5.2    Line 136, second-order windward format should be upward discretization.

5.3    Tittle should exclude Fluent. Could be a CFD study etc.

6.       The authors should supply 1 reference where the FLUENT software is presented/validated. For example website, official user guide.

7.       Verification details in table 1 should be given. Could it be the same size of the research?

Are the physical model test of the annular flume at the University of Shanghai is identical to the annular flume at Hohai University?

 8.       For results part, it very confusing to distinguish the key findings in figures 4, 5, and 8. Velocity vectors or Streamlines are recommend to present the results. Figure 5, the vector bars (scales) should be given.

9.       Languages

Page 2 line 46, hot spots could be revised as hot research topic.

Line 138, a smaller time The time step is set to 0.001s…

10.    References format should be revised.

Journal name of 21 is not given. Since this reference is very important to represent the details of the physical model of the circular flume.

Author Response

Dear reviewers, we appreciate your critical comments on this study.Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The abstract is written well. The authors shall mention the methodology in brief i.e. which size of the annular flume speed ratio was tested.

In the introduction, the authors have described earlier models developed by Su-Hyun Yang and Olya Skulovich. But the drawbacks or limitations of these models are not clear.

Line 77: “lot of research results on 3D numerical simulations of annular flumes in recent years” – authors should summarise the research conducted by other scientists. Explain the knowledge gap, and why the need arise to again take this research project despite a lot of research was already been conducted.

Hypothesis and expected new knowledge are not written.

Line 87: Sentence is incomplete.

Figure 7: what is x/m?

Figure 9: unit is missing.

In conclusion, the discussion about the research findings are mentioned. These findings should be written under discussion.

In conclusion, authors should write about major finding of the research, how this model is more accurate compared to previous models and what are applications of  the developed model.

Author Response

Dear reviewers, we appreciate your critical comments on this study.Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

The study is aligned with the journal's aim and scope. The main concern is the novelty and contribution of the study, given that you are using commercial software for CFD modeling? 

The manuscript can be re-considered following a major revision as follows: 

General Comments:

Provide a detailed response on the novelty and contribution of the study. 

Provide a detailed response with regard to the appropriateness and robustness of the proposed modeling approach for your study problem. 

The English writing and formatting of the manuscript (text and figures/tables) must be significantly improved. Proofreading of the revised manuscript by a native speaker is suggested. 

 Specific Comments:

The title of the paper should be changed and instead of the software name you should elaborate on the CFD method used for the simulation of flow in an annular flume.

The abstract needs re-writing; you need to discuss the numerical technique used and discuss why your choice is appropriate for modeling flow in annular flow. You mention annular flumes are for modeling sediment transport and particulate pollution, is your numerical model also consider sediment transport? and if so, what technique is used for modeling the sediments and calculating their interactions with the flow. The key results should be discussed in the text without using the current numbered formatting. You are mentioning concepts in the abstract without defining them for the readers, for example, what is speed ratio R? 
The conclusion/contribution of the paper is not relevant/correct; ''The results of the study can provide further theoretical basis for the research on sediment dynamics and its related fields conducted by applying the annular flume.'' - how a flow numerical model can provide 'theoretical basis' for sediment dynamic analysis? what is the main contribution of the paper if you didn't include the sediment transport model? 
Further, the abstract should provide information about the model calibration/validation process/data, as well as the flow/sediment conditions used for modeling. 

Keywords should include the CFD technique used for the modeling. 

The Introduction is too brief, and the literature review should be enhanced. A gap analysis and justification for research needs are required. 
More in-depth information about previous numerical modeling studies is required, for example, you need to provide a discussion on the numerical technique used for the simulations and the limitations/deficiencies in the existing models which led to this study. 
One of the most important discussion points about the necessity/importance of annular flumes for pollution transport research would be their applicability for studying biological features in environmental settings, including bedform characteristics and biofilm community development interaction to modify hyporheic exchange (doi.org/10.1016/j.scitotenv.2020.141397). You also missed discussing the appropriateness of annular flumes for modeling particulate pollutants such as microplastics, which is very topical at present (doi.org/10.9753/icce.v36v.papers.63; doi.org/10.1016/j.watres.2019.115337).

The Model Development section will require significant rewriting and enhancement. You need to follow standard section titles, e.g. 'Model Building' --> 'Model Development'. 
'2.1. Simulation object' what is this supposed to mean?
''Mathematical modeling with reference to the physical model of the circular flume at Hohai University [21].'' - This sentence doest make sense, and there are many examples like this in the manuscript which you need to revise.
'2.2. Model selection and control equations' - control equations doesnt make sense, you should use 'governing equations'. The discussion and justifications for the model selection in this section are very weak. I suppose you used RANS with k-epsilon turbulence model, but the RANS bit is not clear. You are not providing references to previous studies that used such a model successfully (e.g. doi.org/10.1016/j.ecoleng.2022.106702; doi.org/10.1016/j.jwpe.2020.101411). Another question is, why did you use RANS and k-epsilon model rather than LES models which can provide detailed information on turbulence characteristics (doi.org/10.1038/s41598-020-68830-5) or SPH-type models? You need to provide overall information on the modeling paradigms available and then justify why the proposed model was selected. 
''2.4 Grid Irrelevance Analysis'' should be 'grid dependency analysis'

'Figure 3. Comparison of simulation and test results' the axis description format should be change (for all the figures), so that you have: parameter (unit), e.g. v (m/s)

3. Simulation results and analysis section doesn't have sufficient discussions and a clear description of the results. e.g. Fig 4 is not clear and I am not sure what section we are looking at. description and discussion of the contour line results shown in the figure are not presented. 

Fig 4 and Fig 5 are the same, you need to combine the two figures. 

Fig 6 - how did you determine the secondary flow intensity? where are the discussions for this figure? and how the results relate to the existing numerical modeling data?

Fig 7 - what is the meaning of different lines? discussions on Fig 7? how do the results compare to the existing studies?

Fig 8 and 9 - what is the significance of these figures? Fig 8 is not cited in the text! this is not acceptable quality for publication, and the section and quality of results and analysis should be enhanced. 

Author Response

Dear reviewers, we appreciate your critical comments on this study.Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 4 Report

Here you can find my comments:

OVERALL: Please, enlarge and re-arrange font sizes to guide the reader properly in all sections. All figures must be composed of HD images. It is mandatory to improve the scientific quality of the whole manuscript.

Please, pay attention to the journal template within the entire manuscript: in all sections, including tables, references, captions, units, equations, and figures.

INTRODUCTION: Please, consider in the scientific background of your study the value of uncertainty quantification in post-processing of both numerical and experimental analysis corresponding to water resources (i.e., https://doi.org/10.1080/24705357.2021.1938255 - https://doi.org/10.3390/agronomy11122458 - https://doi.org/10.1109/MetroAgriFor.2019.8909233 - https://doi.org/10.1016/j.oceaneng.2021.110467 ).

METHODS: Please, explain in detail all the steps used for mesh processing, especially in terms of time cost.

Author Response

Dear reviewers, we appreciate your critical comments on this study.Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 5 Report

The topic of the article is interesting and stimulating. Here you can find my comments:

OVERALL:

- Please, improve the image quality in all figures, a better resolution can be used to ease the data reading.

- Please, insert all corrected axes and labels. The variables and axis should be in a dimensionless form to increase the universality of your data and ease comparison.

INTRODUCTION:

Please, consider a broader background of your study in the context of monitoring and management of natural resources. The authors are invited to check the following papers that are relevant to the study:

Lama, G.F.C., Errico, A., Francalanci, S., Solari, L., Chirico, G.B., Preti, F. 2020. Hydraulic Modeling of Field Experiments in a Drainage Channel Under Different Riparian Vegetation Scenarios. In Innovative Biosystems Engineering for Sustainable Agriculture, Forestry and Food Production; Coppola A., Di Renzo G., Altieri G., D’Antonio P., Eds.; Springer: Cham, Switzerland, 2020; 69–77; doi:10.1007/978-3-030-39299-4_8.

Khan, M.A., Sharma, N., Lama, G.F.C., Hasan, M., Garg, R., Busico, G., Alharbi, R.S. 2022. Three-Dimensional Hole Size (3DHS) Approach for Water Flow Turbulence Analysis over Emerging Sand Bars: Flume-Scale Experiments. Water 14, 1889. https://doi.org/10.3390/w14121889.

de Oliveira, L. E., & Janzen, J. G. (2020). Mass Exchange in Dead Water Zones: A Numerical Approach. In Water, Energy and Food Nexus in the Context of Strategies for Climate Change Mitigation (pp. 59-68). Springer, Cham. doi:10.1007/978-3-030-57235-8_5.

Lama, G.F.C., Sadeghifar, T., Azad, M.T., Sihag, P., Kisi, O. 2022. On the Indirect Estimation of Wind Wave Heights over the Southern Coasts of Caspian Sea: A Comparative Analysis. Water 4, 843. https://doi.org/10.3390/w1406084)

METHODS:

- Some model choices should be described, and examples given to demonstrate the accuracy of the method. For example, the rigid-lid approximation (symmetry plane on the top) requires a citation of a Froude number threshold and an example of it being used in the numerical simulation context. Please check the following:

de Oliveira, L.E.D.; da Costa, F.R.; Gualtieri, C.; Janzen, J.G. Effects of Vegetation Density on Sediment Transport in Lateral Cavities. Environ. Sci. Proc. 2022, 21, 16. https://doi.org/10.3390/environsciproc2022021016

- The order of the subsections should be changed. The choice of the grid and its characteristics should be presented before the Grid Convergence section.

- More information should be presented about the computational effort required to calculate the numerical model. This description must include the hardware and wall time needed.

Other suggestions are indicated in the attached file. I hope that these comments can improve the quality of the manuscript and highlight the scientific relevance of the text. For these reasons, I suggest that the paper must go through a minor revision.

Comments for author File: Comments.pdf

Author Response

Dear reviewers, we appreciate your critical comments on this study.Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have made some changes that they thought was tried their best to. I agree to accept this manuscript.

Author Response

Thank you for your continued support of this paper and have a great life!

Reviewer 3 Report

The authors have revised the manuscript and addressed some comments while there are still outstanding comments/ revisions from the first review to be completed. Revise the manuscript according to the below comments. 

The Introduction and the literature review should be enhanced. A gap analysis and justification for research needs are required. All you did to address my comment was adding a paragraph in the revised manuscript. The literature and discussion porposed is not implemented, specifically: 
One of the most important discussion points about the necessity/importance of annular flumes for pollution transport research would be their applicability for studying biological features in environmental settings, including bedform characteristics and biofilm community development interaction to modify hyporheic exchange (doi.org/10.1016/j.scitotenv.2020.141397). You also missed discussing the appropriateness of annular flumes for modeling particulate pollutants such as microplastics, which is very topical at present (doi.org/10.9753/icce.v36v.papers.63; and doi.org/10.1016/j.watres.2019.115337).

The Model Development section will require significant rewriting and enhancement. 
'2.2. Model selection and control equations' - control equations doesnt make sense, you should use 'governing equations'. The discussion and justifications for the model selection in this section are very weak. I suppose you used RANS with k-epsilon turbulence model, but the RANS bit is not clear. You are not providing references to previous studies that used such a model successfully (e.g. doi.org/10.1016/j.ecoleng.2022.106702; doi.org/10.1016/j.jwpe.2020.101411). Another question is, why did you use RANS and k-epsilon model rather than LES models which can provide detailed information on turbulence characteristics (doi.org/10.1038/s41598-020-68830-5) or SPH-type models? You need to provide overall information on the modeling paradigms available and then justify why the proposed model was selected. 

The above discussions should be added to the manuscript together with the refereances.

Author Response

Dear reviewers, please see the attached document.

Author Response File: Author Response.pdf

Reviewer 4 Report

Author Response

Dear reviewers, please see the attached document.

Author Response File: Author Response.pdf

Reviewer 5 Report

Overall, the paper improved but some small changes are still required. Some figures could be placed in a higher resolution and the smaller comments are present in the text. Furthermore, I think the authors could benefit from reading the following papers:

-        Lama, G.F.C., Crimaldi, M., De Vivo, A., Chirico, G.B., Sarghini, F. 2021. Eco-hydrodynamic characterization of vegetated flows derived by UAV-based imagery, 2021 IEEE International Workshop on Metrology for Agriculture and Forestry (MetroAgriFor), 273–278, doi:10.1109/MetroAgriFor52389.2021.9628749.

-        Box, W., Järvelä, J., Västilä, K. 2021. Flow resistance of floodplain vegetation mixtures for modelling river flows. Journal of Hydrology, 601, 126593.

-        Lama, G.F.C., Rillo Migliorini Giovannini, M., Errico, A., Mirzaei, S., Chirico, G.B., Preti, F. 2021. The impacts of Nature Based Solutions (NBS) on vegetated flows’ dynamics in urban areas, 2021 IEEE International Workshop on Metrology for Agriculture and Forestry (MetroAgriFor), 2021, 58–63. doi:10.1109/MetroAgriFor52389.2021.9628438.

-        de Oliveira, L.E.D., Janzen, J.G. (2020). Mass Exchange in Dead Water Zones: A Numerical Approach. In: Leal Filho, W., de Andrade Guerra, J.B.S. (eds) Water, Energy and Food Nexus in the Context of Strategies for Climate Change Mitigation. Climate Change Management. Springer, Cham. https://doi.org/10.1007/978-3-030-57235-8_5

Comments for author File: Comments.pdf

Author Response

Dear reviewers, please see the attached document.

Author Response File: Author Response.pdf

Round 3

Reviewer 3 Report

The authors have revised the manuscript, but my comments are not addressed in the manuscript, or in the response letter.  Overall, the manuscript is improved compared to the first submitted draft. 

Language edit is required. 

Author Response

Dear Reviewers:
  Thank you very much for your efforts on this article. We have taken into account your suggestions to correct the article grammar and other issues at the official MDPI institution. Please see the attachment for the official proof.

Author Response File: Author Response.pdf