Review Reports

Round 1

Reviewer 1 Report

A lot of work to be done to make the text clear and understandable.

See my comments in attached pdf file.

Figure 2 must be improved.

Some reference works to be added in the introduction (as Hirschel's AIAA book and G. Sutton's book).

Comments for author File: Comments.pdf

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

General comment:

The manuscript is a high quality work including new results. The paper presents the results of the study the flow characteristics of the nozzle with large expansion ratio and its influence on the force on the nozzle. In order to observe the flow separation phenomenon and the pressure distribution on the nozzle wall, the cold flow test under ground condition was carried out. The separation point under different pressure and the pressure pulsation characteristics on the nozzle wall before and after the separation point were obtained. Then the numerical simulation of separation fluid field was carried out. The experimental and the numerical simulation results were in good agreement. In the next part of the work, the fluid-structure coupling analysis was carried out on full-scale nozzle. The obtained results show the difference of the flow field distribution under ground and high altitude environment. The nozzle deformation properties under the separation condition was studied.

The results obtained by the Authors are very interesting and important in the design of rocket engine nozzles.

Detailed comments:

1. In the introduction, there is no clear indication of what is novelty in the work. Authors should provide information (a few thoughts) about what new elements their work contains, referring to the knowledge in the researched field.

2. How to define ‘Large expansion ratio’? Could you please give the definition?

3. Experimental test bench: the Authors should give details of specification of the experimental apparatus, such as the sensitivity. The Authors need to include uncertainty and error analysis for measurement.

4. Can the authors justify the choice of inlet pressure during the tests? Have you considered testing at higher total inlet pressures?

Best regards

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 3 Report

The study discusses numerical and experimental flow separation characteristics with large expansion ratios at the ground and higher altitudes. The following observation suggestion may help improve the manuscript.

·       The Author should avoid very large sentences using commas and semicolons. Revise the complete manuscript.

·       Mention the value of the expansion ratio in the abstract.

·       The abstract may be further revised by adding quantitative results rather than qualitative explanations.

·       The Author should avoid bulk citations without mentioning actual contributions in research articles. For example, [1-4]; [5-8];10-15]; [16-21], etc.

·       In lines 48-49, the Author should mention the pressure ratio value instead of saying a certain pressure ratio.

·       The article missed the gap between research and novelty; the Author should incorporate it based on the literature study.

·       It seems the Author missed the Reference to Figure 1.

·       In the experimental study, the Author needs to mention each measuring instrument's range and uncertainty.

·       What was the nozzle design condition with assumption? Also, mention the geometrical specification of the nozzle.

·       In figure 5, the Author can also add plots for other inlet's total pressure for better understanding and comparisons.

·       Line 132: instead of writing "some laws," the Author should write the name of the law.

·       The Author should also mention the design Mach number of the nozzle.

·       Line 147:  instead of writing "high quality," the Author should mention the value based on which concluded high-quality mesh.

·       The boundary conditions value of each needs to be mentioned in the manuscript.

·       In the numerical study, the tool used for analysis needs to be mentioned along with its version. Also, discuss the basis of the turbulence model selection and convergence criteria.

·       Question 1, needs to be referenced.

·       At higher altitudes mentioning only pressure is not sufficient as flow is compressible. It is recommended to mention the temperature along with the value of altitude.

·       In Figures 11 and 12, the Author should write "Legend" in English only.

·       Line 195; what is ε? It needs to be mentioned with its importance.

·       In my view, Figure 17 is not needed. Figure 7 and 18 is sufficient to show the mesh.

·       Line 287: At the place" Fluent," the Author should mention ANSYS-Fluent with the version.

·       Line 312. Mention the Figure number.

 

·       In Reference, the Author should avoid writing [J] at the end title of the journal. The Author may refer to Journal guidelines.

 

Author Response

Please see the attachment.

Author Response File: Author Response.docx