Dynamic Characteristics of Unsteady Aerodynamic Pressure on an Enclosed Housing for Sound Emission Alleviation Caused by a Passing High-Speed Train

Round 1

Reviewer 1 Report

This manuscript reports the numerical simulation analysis of high-speed trains considering enclosed sound barriers to further reduce noise. The research is both scientifically and technologically interesting, as well as having direct industrial ramifications. The models utilized in the study, as well as the techniques and simulation steps, are all explicitly described. The results are thoroughly discussed, producing important outcomes for the conclusion section. In sum, in this sense, I recommend this manuscript for publishing after a minor revision.

• In the title, although the authors mentioned “Dynamic characteristics” of flow around high-speed train is considered, but only pressure distribution and PSD were discussed in the result section. If possible, provide an explanation about unsteady flow characteristics such as vorticity field, turbulent kinetic energy, velocity, streamlines, and boundary layer for the high turbulence flow of this paper.
• Please review the paper again, improve and correct sentences as you can, especially the abstract part. In abstract: some mistakes in the spelling of the word like” param-eter, compli-cated, pe-riodic” and sentence like” This train-induced wind pressure, particularly its dynamic characteristics, is a key param-eter in structural design.”
• “dynamic layering method” that is used in Ansys Fluent dynamic mesh box is not the general method for numerical simulation. Please correct the sentence.
• "Numerical simulation, pressure distribution" is such a broad term. Please choose a more specific word to make the document in search more well-known and specialized.
• Introduction part is well organized and explained. Just add reference about the employed train “CRH380” and also rewrite the last paragraph that is overall look in this manuscript.
• The quality of the figures should be improved as much as possible and add some more explanation.

For instance, in Fig. 1 (a), please show the full body of the train with all dimensions on it, and Fig. 1 (b) add the dimension of track spacing and ... 

In Fig. 2, please fully characterize, like add dimension of two acceleration domains at both ends with a length of 550 m …

In Fig. 10, in the caption instead of Time/ s please correct time(s).

In Fig. 11(b), is so confusing. Please improve it if possible.

• In Fig.2, for the B.C of pressure outlet please explain more. Is it an atmospheric condition? “ while the other five surfaces are set as outlets with zero pressure.” and …also add some reference that implemented with this B.C.
• Please explain more about the computational costs, number of used core, number of mesh in full case ( not just for the validation case), yPlus, the ratio of the mesh (if used) and other information like this. It helps the reader have a correct perception of the computational domain for implementing similar simulations.
• Time step size is defined as 2e-3s during the simulation. Have the authors investigated the impact of time step size on the predicted results? Please discuss.
• Convergence evaluation is an important issue, and thus the convergence criterion should be given more clearly.
• It is correct that finding a case for validation of this complex case and flow is difficult. But, now the regime of the validated case (3. 0 m/s) and the current work (350 km/h) is highly different. If possible, please add some explanation. “Two different meshes with different numbers of cells were divided: 266
• coarse meshes (24 million) and fine meshes (32 million).” If these number is for validation case, please mention.10- The dominant frequency in Fig. 17, calculated by data how many points during the which time simulation?
• As previously mentioned, the author may go into greater depth on turbulence parameters, not just pressure distribution, for the fully turbulent flow of the case in this research.

Comments for author File: Comments.docx

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

Introduction

The introduction seems to be only a sequence of numerous experimental and numerical studies. An introduction with a focus on the aerodynamic effects of high-speed trains passing sound barrier tunnels would be more beneficial for the readers to be introduced in this topic. Furthermore, the motivation based on shortcomings of the cited literature would be then more comprehensible.

Methods

The method includes all relevant information. Only the Reynolds number, the y+ boundary resolution and the CFL number would also be of interest. Regarding the structure, the description of the mesh independence study should be included in the mesh section.

Figure 5: The correct denomination of the pressure sectors S1-S11 used in the text should be included in the figure.

Results

The captions of all figures should include all relevant information especially the parameter shown. Thus, all caption should be extended with all information that the figure or table can be evaluated without needing to read the text. Furthermore, the running text can then be shortened by the technical description of the figures which makes the running text more readable.

Figure 11b is not to understand. No color is explained in in the caption and the description in the text is not helpful. A suggestion is to additionally show a figure with the train and the pressure/density field as color contour plot to explain the wave front dynamics. Additionally, the authors should provide a supplement video of the train transition with pressure or density shown.

Another question is how large the wave propagation speed and whether the waves have acoustic characteristics or are purely hydrodynamic?

Line 357: Td --> "d" should be written as subscript.

In figure 16, the radial position of the pressure probes along the tunnel contour are not indicated. The same applies for the power spectra in fig. 17.

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

The paper addresses investigations of interest with respect to the pressure impact on the housing due to the impact of a high speed train moving through the housing.

The following points should be considered prior to publication:

Figure 5:

The absolute dimensions of the housing should be also indicated as relative dimensions with respect to the typical dimensions of the vehicle (train) considered.

Figures and graphics, e.g. Figs. 10, 11, ...:

Of course, dimensional data are of interest for the cases shown but it is also recommended to add on the upper x- and right y-line of the graphs non-dimensional quantities with respect to characteristic time scales and pressure coefficients or relative peak pressures, respectively.

Adding typical characteristic (representative non-dimensional) quantities is of particular relevance for a more general description of the effects.

Further, the wording partially used should be critically checked for the respective meaning. For the reviewer, the term "sound barrier" is associated with a completely different meaning as it is used here. Here, effects due to a housing dedicated to sound emission alleviation are investigated. Also, the term "wind pressure" is quite special. Typically, static, dynamic or total pressures are terms used in fluid mechanics. Consequently, the whole article should be checked for proper wording in the context of the problem studied.

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

The authors have addressed the reviewer's comments to some extent.

The reviewer still strongly recommends to exhange the term "sound barrier" by a term like "noise protection housing" or "housing for sound imission alleviation".

Author Response

Thank the reviewer for the valuable suggestions. The term "sound barrier" has been revised as “housing for sound imission alleviation” in the revised manuscript. Thanks!

Author Response File: Author Response.pdf