Numerical Simulation of Pollutant Spread in a Double-Deck Viaduct

Round 1

Reviewer 1 Report

This is an interesting numerical study on the simulation of pollutant spread in a double-deck viaduct. It merits publication in Sustainability once a number of issues are addressed. More specifically:

 

1. In the Introduction, the authors need to more clearly explain the contribution of their work in the literature as well as the differences between their work and previous relevant studies.

 

2. Lines 33-65: the text needs to be better structured and broken into fully-fledged sentences and paragraphs, so that it is easer to read/understand.

 

3. Lines 86-87 “due to 86 distance restrictions,”: please explain what is meant here

 

4. Section 2.1: why this wind direction was selected?

 

5. Final geometrical and mess details of the simulation domain could be presented in an overall Table.

 

6. There is overlap between sections 2.2. and 2.6 especially regarding teh LES versus k-ε model discussion. Sections could be merged or at least overlaps deleted.

 

7. Section 2.6: were the authors involved in this validation. If they use existing validations this should be clearly sated and the section could be shortened, since the manuscript should focus on the authors’ own work.

 

8. The study presents a very specific case, and the validation presented is a general one for the model’s performance in canyon flows. The authors should better reflect the usefulness and contribution of the present manuscript: not only in the Introduction, but also in the Conclusions, noting what is the practical implications of the information presented in the Conclusions section.

 

Very minor editing needed.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

1. The main question addressed by the research is to estimate the spatial distribution of carbon monoxide concentration over street canyon with double-decker flyover, taking into account the effects street canyon geometry and wind velocity. Within the research authors used CFD method and the well-known RNG k-ε turbulence model (Yakhot and Orszag 1986).

2. The topic of modeling the distribution of air pollutants in the atmosphere based on Navier-Stokes equations isn't really original. However, the research addresses a particular problem of this scientific topic.

3. The authors discovered some patterns of distribution of gaseous pollutant concentration for the described specific conditions and geometry of street canyons with double-deck traffic arteries. The feasibility of the study and obtained results could be justified if such double-decker flyovers constructed among high-rise buildings are in common occurrence.

4. It would be desirable to consider the case of a non-stationary problem with time integration.

5. The references are appropriate. But it would be good to greater representation of American, European, Russian etc. authors. 

6. All figures have low resolution. Figures 7, 9 and 11 contain very small text lables. Therefore, values of CO concentration and wind velocity indicated in these figures are almost unreadable. It is advisable to replace these images with better quality ones.

7. It would be desirable to clarify how exactly the RNG k-ε model was implemented in order to run computations: authors' own cade, Matlab, Comsol Multiphysics or something else.

The manuscript contains plenty of very long sentences that are difficult to comprehend right away.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

The authors presented a numerical study on the pollutant spread in a double-deck viaduct.

The main quantitative results are to be presented in the abstract.

The novelty of the paper is to be clearly stated.

Use ‘’nomenclature’’ instead of ’’Table 1. List of symbols’’

What is the used CFD software?

The used turbulence model is to be justified.

What is the considered range for Reynold number?

Is it realistic to consider the problem as 2D?

The dimensions of the computational domain should be justified.

The font size of the text of Fig 5 is very small. The same goes for fig 7.

Use ‘’streamlines’’ instead of ‘’ Flow lines’’

The scientific soundness should be improved by adding physical interpretations to the discussion.

English level should be improved.

The following paper may be added to the literature review:

10.3390/math10071118

English level should be improved.

 

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

I would like to thank the authors for the responses to the referree's comments.

The following two comments in the original manuscript need to also be addressed in the text of the manuscript (and not only in the cover letter response). I attach below my comments and the responses of the authors for ease of reference:

Point 3：Lines 86-87 “due to 86 distance restrictions,”: please explain what is meant here.

The distance limit refers to the width of the street, when the street is wide, wider viaducts can be built instead of double layers, and when the street is narrow, double layers of viaducts can be built to ease traffic.

Point 4：Section 2.1: why this wind direction was selected?

The wind direction chosen in the study is perpendicular to the street valley, which is more convenient for setting and closer to reality.

A last review is needed, especially in the new parts of the revised manuscript.

Author Response

Thank you very much for your comments. We have revised the manuscript based on your suggestions. We carefully reviewed the full text, especially the revised contents.

Reviewer 3 Report

After revision, the paper can be accepted for publication 

Author Response

Thank you very much for your comment. We wish you in good health.