Effects of Inclined Interface Angle on Compressible Rayleigh–Taylor Instability: A Numerical Study Based on the Discrete Boltzmann Method

Round 1

Reviewer 1 Report

In this work, the effect of inclined interface angle on compressible Rayleigh-Taylor instability is investigated by using the discrete Boltzmann method, and both the thermodynamic non-equilibrium (TNE) and hydrodynamic non-equilibrium (HNE) effects are analyzed in detail. The results of this study provide some new physical insights on the problem of RT instability under inclined interface. Overall, the paper is well-written and can be accepted for publication in Entropy. However, I would appreciate if the authors could submit a revision that takes into account the following points:

1. It would be better if the title is modified by ‘Effects of inclined interface angle on compressible Rayleigh-Taylor instability: A numerical study based on the discrete Boltzmann method’.

2. It should be noted that "the nonorganized energy fluxes" and "the non-organized energy fluxes" are used in this paper, please choose one of the forms and keep it throughout the text.

3. Line 47: Please provide the full name of NS

4. In the introduction section, more "the effect of" are used. If possible, please use other synonyms to replace it.

5. Line 223: Is it "g = −2.0" or "−g = −2.0"?

6. Line 267:"and the second mechanism and the third mechanism offset each other, so the |_y| decrease."-->"and the second mechanism and the third mechanism offset each other, thus the |_y| decreases."

7. Line 277-281: The following paragraph is too long, please rephrase it. "The physical reason for the first decrease of D₂ is that, in the initial phase, the disturbance waves on both sides of the material interface propagate to both sides, and the amplitude and macroscopic physical gradient of the flow velocity near the disturbance wave decrease with time."

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript studies the effects of inclined interface angle on compressibleRayleigh-Taylor (RT) instability using the discrete Boltzmann method (DBM). Its contribution lies in using the DBM to study thermodynamic nonequilibrium effects in RT, in contrast with most of the literature that focus only on hydrodynamic nonequilibrium effects. It is found that, on the whole, the TNE strength firstly increase and decrease afterwards. What’s more, the larger the initial interface inclinationangle is, the faster the RT evolves. The simulations seem to be well implemented and the results seem correct. I recommend the manuscript for publication. However, there are some other questions I’m interested in.

1.    What are the advantages of two-component DBM over single-component DBM? Please give more discussion.

2.    What is the formula for calculating vorticity?

3.    In line 260, the authors mentioned that "The disturbance wave gradient will decrease with time". How is the perturbation wave formed? Please give an explanation.

The manuscript studies the effects of inclined interface angle on compressibleRayleigh-Taylor (RT) instability using the discrete Boltzmann method (DBM). Its contribution lies in using the DBM to study thermodynamic nonequilibrium effects in RT, in contrast with most of the literature that focus only on hydrodynamic nonequilibrium effects. It is found that, on the whole, the TNE strength firstly increase and decrease afterwards. What’s more, the larger the initial interface inclinationangle is, the faster the RT evolves. The simulations seem to be well implemented and the results seem correct. I recommend the manuscript for publication. However, there are some other questions I’m interested in.

1.    What are the advantages of two-component DBM over single-component DBM? Please give more discussion.

2.    What is the formula for calculating vorticity?

3.    In line 260, the authors mentioned that "The disturbance wave gradient will decrease with time". How is the perturbation wave formed? Please give an explanation.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

The authors studied the impact of an inclined interface on compressible Rayleigh-Taylor instability. The evolution of global average density gradients and some non-equilibrium quantities are studied and the possible underlying physical mechanism is discussed in the manuscript. This work adds valuable information to the understanding of compressible Rayleigh-Taylor instability with an inclined interface. However, the validation of the method and the descriptions of some plots are not sufficient or even missing. Therefore, I would not recommend the publication of the manuscript in its current state. Here I listed some comments which may help the authors to improve.

Major points: 

1. A validation of the simulation method against theoretical analysis and/or experimental results is missing. For example, the authors can validate their simulation method via comparison with existing literature (theoretical or experimental studies) on compressible Rayleigh-Taylor instability with a non-inclined interface.

2. Each plot shall have a corresponding description in the main text. However, the description of some plots is missing, for example, Fig. 6c, 6d, 8c, 8d, 10c, 10d, etc.

3. The simulations are performed in 2D. What is the effect of 3D on the conclusions drawn in this manuscript?

4. Is the interface a sharp interface or a diffusive interface? In the case of a diffusive interface, what is the thickness of the interface and what is the effect of interface thickness on the results?

The texts need careful proof-reading to avoid grammar mistakes.

For example, in line 210, "where the subscript m the material interface, θ the inclination angle of the initial interface" shall be corrected to, for example, "where the subscript m represents the material interface, and θ denotes the inclination angle of the initial interface."

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

The authors have successfully addressed my comments.