3D CFD Analysis of Natural Ventilation in Reduced Scale Model of Compost Bedded Pack Barn for Dairy Cows

Round 1

Reviewer 1 Report

The authors present a numerical and experimental analysis of flow (air ventilation) in and around a barn building. The numerical model employs a RANS based approach to resolve turbulence. Governing equations seem to be repeated, Eqns 2 and 3. The paper suffers from these major issues:

 

1- There seems to be no linkage between the num and exp work. Was exp study done to validate the num model? If so, why such validation analysis is missing?  

2- The governing equations are for compressible flows. Such flows can occur at Ma numbers greater than 0.3 or at wind speeds of 0.3 of the speed of sound or higher. What is the justification for such num modeling approach?

3- It is hard to comprehend whether Figs. 7 to 11 are numerical or exp results. The captions of all figures are not comprehensive in explaining what is being plotted.

4- ONce again, where are the exp data/results. They are no presented appropriately. 

5- the objective of the paper is unclear and vague. It is mention in the last paragraph of the introduction that the goal of the paper is to develop a numerical model of barn ventilation. There is no model development because a commercial code is used  -- without a rigorous validation.  This is a serious problem with the paper. 

 

Due to these issues, I would not suggest the paper to be accepted in its current form.

 

Author Response

Dear Reviewer, 

 

All corrections were made according to the understanding of the questions.

 

We added the analysis of the real data with the simulated data (Figure 14).

Thank you for contributing to the improvement of our study

Author Response File: Author Response.pdf

Reviewer 2 Report

Dear Authors,

this is generally a good written paper, but there are a lot of open questions:

• It is not clear, what is the size of the test section in the wind tunnel. This affects the results in general and the comparison with CFD results.
• You stated 0.41 m/s for highest deviation between CFD and wind tunnel test. For 1.0 m/s wind speed it would be more than 40 %, which is very high, not a good agreement. For 0.1 m/s wind speed it is more than 400 %, unacceptable. However, in the paper only the results for wind speed 0.1 m/s are presented. The results of the higher wind speed are missing.
• 12 is inconsistent with stated wind speed 0.1 m/s or 1.0 m/s.
• The chosen wind speeds for the scale model correspond 0.00625 and 0.0625 m/s wind speed in the reality. To my mind it is no “wind”, but the community should decide if these are representative values, or not.
• The computational domain is very small. It is stated, that this is crucial, but its investigation is missing.
• Mass flow rate at the compost bed is unphysical and very large. Especially as you stated, that the generation of gas and moisture is negligible. As the computational domain is quite small in relation to the barn, this mass flow rate is in similar range as the mass flow rate prescribed at the inlet boundary.
• Boundary layer: the wind velocity changes from the ground upwards very rapidly and has significant impact onto the results. This effect was completely ignored in the wind tunnel test as well as in the CFD simulation. The comparison of the results from CFD and experiment is still valid, but the adaption of these to real barn is incorrect.

Please consider additionally the notes in the attached PDF file.

Comments for author File: Comments.pdf

Author Response

Dear Reviewer,

 

All corrections were made according to the understanding of the questions.

 

We added the analysis of the real data with the simulated data (Figure 14).

Thank you for contributing to the improvement of our study.

 

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

None.

Author Response

Dear reviewer,

We are grateful for your consideration of this manuscript, and we also very much appreciate your suggestions, which have been very helpful in improving the manuscript. We also thank for their careful reading of our text.

All the comments we received on this study have been taken into account in improving the quality of the article, and we present our reply to each of them separately.

Author Response File: Author Response.pdf

Reviewer 2 Report

Dear Authors,

consider please the notes in the attached PDF file.

The major deficits:

• you validated the model for laminar flow, but not for turbulent flows
• you claim you measure laminar flow in wind tunnel and simulate turbulent flow, it is inconsistant
• the prescription of velocity of 0.04 m/s at the compost area is unphysical
• the absolut error of 0.41 m/s is high, it is not a good model
• The model accuracy is probably influenced by the improper small size of the computational domain
• Figure 13 completely inconsistant with the descriptions in the paper
• The mention of the Froude number is improper

Comments for author File: Comments.pdf

Author Response

Dear reviewer,

We are grateful for your consideration of this manuscript, and we also very much appreciate your suggestions, which have been very helpful in improving the manuscript. We also thank for their careful reading of our text.

All the comments we received on this study have been taken into account in improving the quality of the article, and we present our reply to each of them separately.

Author Response File: Author Response.pdf

Round 3

Reviewer 2 Report

Dear Authors,

there have been good imporvements made.

The mention of the plexiglas is crucial. Is in the real barn any similar part at this position? If not, then for the E-W wind direction there is a great discrepancy between model and real geometry.

Lines 290-297: If you prescribe for the velocity at the inlet boundary 0.04 m/s, it corresponds a real wind speed of 0.04/16=0,0025 m/s. The question is, what is the relation to the wind speed of 0.1 m/s in the wind tunnel test? This is very confusing: you state, that the velocity at the inlet is 0.1 m/s but (newly) in every figure one can see 0.04 m/s.

(In Figure 13 one can see, that some calculations are not finished.)

 

Author Response

Dear reviewers,

We thank you very much for your interest in our manuscript. We appreciate your consideration of its strengths and its potential for improvement. The comments made by the editorial conference and the peer reviewers are very valuable to us and we gladly considered them in the revision of our review. Please find our responses below in pdf file.

 

Thanks

Author Response File: Author Response.pdf