Thermal Protection Mechanism of a Novel Adjustable Non-Ablative Thermal Protection System for Hypersonic Vehicles
Round 1
Reviewer 1 Report
Summary of the Work
The authors proposed a thermal protection system (TPS) with the objective to counteract the reduction of the global thermal protection performance of the system when the windward side of the hypersonic vehicles has a non-zero angle of attack. To this aim, they proposed an adjustable non-ablative TPS for this problem and studied the mechanism of improving global thermal protection performance. The novelty of the authors’ mechanism consists in using a spike that is not co-axial with the nose cone and the spike can rotate in the direction of the free stream. The mechanism and optimal installation angle have been investigated numerically.
General Considerations
- In 20199, two of the authors have already produced a work in the field of "Non-ablative thermal protection system with combined spike and opposing jet concept" (paper not quoted in the list of References).
- Please, check the English of the manuscript; several typos have been detected.
- Please, ensure that all the acronyms are duly specified when they appear for the first time in the document even if they are well-known in the literature (e.g., the acronym TPS=Thermal Protection System in the Abstract is not specified).
- The manuscript is written in a clear way; I have enjoyed reading it.
Suggestions
1) Angle θ is shown in Figure 1. Please, define θ also in the text of the manuscript.
2) Figures 3., 5., 7., and 9. show the numerical simulations of the model proposed by the authors (ref. to Figure 1.). The governing equations of the model are not reported in the manuscript.
2i) For clarity, could the authors show these equations, give a brief description of them, or post a brief discussion about them?
2ii) In general, such problems require the solution of difficult boundary-value equations. How was this problem addressed?
3) For completeness, please explain in a nutshell why it is important to evaluate the Mach number distribution to perform aerodynamic heating analysis. Please, show, very briefly, how this number has been (numerically) calculated.
4) In Section 2. the authors showed their physical model and illustrated the numerical results. In particular, the authors determined numerically the optimal installation angle and established that, for their model, the difference between the angle of attack and the optimal installation angle is about 2.4°. However, please
4i) provide a physical interpretation of their numerical findings;
4ii) explain why is there an optimal angle;
4iii) explain why the heat flux distribution of the nose cone is bell-shaped;
4iv) explain, from the physical point of view, why the heat flux tends to vanish as the θ values increase (see Figure 6.a).
It is clear that being able to answer the above questions would be really helpful in practice.
5i) Please, specify the relative errors of Qw in Figures 4., 6.a, 8., 10., and 11.a.
5ii) Please, specify the relative errors of θw in Figures 6.b and 11.b.
Conclusions
As said, I enjoyed the work. However, there are some points which, in my opinion, need to be clarified. Furthermore, the equations governing the system are neither reported nor discussed. The physical interpretation of the results obtained numerically is missing. This could be grounds for objection. I encourage the authors to heed the above-mentioned suggestions.
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Page 2 : It seems that there are lots of previous stduies on "Spike and Jet" system. Why the authors didn't make any validation stduies by comparing well-known experimental data (or other researchers computational results) and their numerical results? I believe that mesh sensitivity study can not guarantee the accuracy and reliability of the numerical method.
Page 2 : It seems that L1, L2, D1, D2 in Figure 1 are not in the right scale. L1 is 5mm and D1 is 4mm in Table 1, but L1 is much bigger than D1 in Fig. 1.
Also need to check the definition of angle "theta". In Figure 1, (+) is in CW direction but CCW in Figure 6.
Page 2 : Please fill out all the blanks in table 2.
Page 3 : In line 71, I guess that the readers of this paper will not have interests the detail number of computational meshes such as 2345856, 3801696 and so on. I believe that 2.3 Mil, 3.8 Mil. would be enough. Same comment on Table 3. and Figure 4.
Page 3 : In figure 2, it seems that the far field location is very close to the nose cone. Why the far field is located in the very near-field?
Page 6 : Please add zero angle of attack results in Figure 6.
-END-
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
The thermal protection mechanism and the optimal installation angle are numerically analyzed to improve the thermal protection performance of the active (adjustable non-ablative) thermal protection system based on the spike and jet. The problem is very useful to the present scientific community. The grid distribution and examination are good. The paper is suitable for publication after incorporating the comments.
Comments:
1. The introduction is not enough. Authors must provide the background of research in detail.
2. Motivation of the present problem is not clearly given. It should be explained in the last paragraph of introduction section.
3. The literature review is inadequate.
4. Explain the physical model in detail (in sec 2)
5. The authors just stated “CFD method’ is used. What numerical method did you use? Need more details.
6. What are the schemes used for different terms in model equations (RANS equations) and Turbulent mode. Explain them in detail.
7. Why the authors take installation angle from 5° to 12°? Is there any specific reason? If we choose other values of installation angle, that is, greater than (>12°) or less than (<5°), what about the results?
8. Add nomenclature for all symbols
Author Response
Response to Reviewer 3 Comments
Point 1: The introduction is not enough. Authors must provide the background of research in detail.
Response 1: The author enhances the introduction part in revised manuscript.
Point 2: Motivation of the present problem is not clearly given. It should be explained in the last paragraph of introduction section.
Response 2: The author has enhanced the motivation of proposing the adjustable non-ablative thermal protection system in the last paragraph of introduction part in revised manuscript.
Point 3: The literature review is inadequate.
Response 3: The author enhances the introduction part, and related descriptions are added in revised manuscript.
Point 4: Explain the physical model in detail (in sec 2)
Response 4: The descriptions on the physical model is added in Section 2 in revised manuscript.
Point 5: The authors just stated “CFD method’ is used. What numerical method did you use? Need more details.
Response 5: The author has enhanced the numerical method in Section 2 in revised manuscript.
Point 6: What are the schemes used for different terms in model equations (RANS equations) and Turbulent mode. Explain them in detail.
Response 6: This paper adopts the computational fluid dynamics (CFD) method based on the Reynolds-Averaged Navier-Stokes equations to analyze the aeroheating, the AUSM+ scheme with second-order accuracy [26] and Menter's SST k-ω turbulent model [27] are chosen.
Point 7: Why the authors take installation angle from 5° to 12°? Is there any specific reason? If we choose other values of installation angle, that is, greater than (>12°) or less than (<5°), what about the results?
Response 7: The reason for choosing installation angle from 5° to 12° is that the optimal installation angle (10.42°) is between 5° and 12°. If the installation angle is greater than 12°or less than 5°, the numerical calculation can not obtain the optimal installation angle.
Point 8: Add nomenclature for all symbols
Response 8: All symbols are expained in revised manuscript.
Author Response File: Author Response.pdf
Round 2
Reviewer 3 Report
The authors made the corrections well. The paper is suitable for publications.
