Aerodynamic Characteristics of the Novel Two-Dimensional Enhanced Shock Vector Nozzle

Round 1

Reviewer 1 Report

Dear Authors,

Thank you for sending me the manuscript “Aerodynamic characteristics of the novel two-dimensional enhanced shock vector nozzle” for revision. The Reviewer has the following comments about the manuscript:

1. The text contains grammatical errors. Please provide corrections.

2. 2.1 Governing equations. Please define the gas model. The Reviewer suspects the ideal gas approach. Why combustion products were not calculated needs to be clarified.

3. 2.1 Governing equations. Please add that the k-omega SST model was used. The simulations are bi-dimensional, but Eq. 1 is three-dimensional.

4. Please define the solution methods of the flow model. Was the simulation made on OpenFoam?

5. 2.3 CFD validation. The topic looks confusing. The Reviewer suggests separating it into geometry sections, boundary conditions, meshing criteria, etc. Please define pressure inlet values set in simulations. 

6. 2.3 CFD validation. “the total temperature of both the mainstream and secondary flow is 300 K”. It is unclear how the Authors obtained thrust at such low total temperatures.

7. The mesh has excellent quality. The images and plots are well-made as well.

8. The main Reviewer’s concern is the computational and geometrical simplicity. The Reviewer remembers similar publications from 20-25 and probably 30 years ago. The thrust control in the supersonic nozzle is an old model widely studied by different authors. From the computational point of view, the current work does not present any novelty. In the Reviewer’s opinion, it is a repetition of an old (reliable and classical, but still old) approach. Quantitative estimations in the authors’ conclusions are related to the geometry and boundary conditions studied and cannot be generalized.

The text contains grammatical errors. Please provide corrections.

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 2 Report

The paper presents a CFD study of fluidic control/thrust vectoring in supersonic nozzles. The work is interesting and the results are compelling and should appear in journal form, once the authors address some of the remaining issues in their manuscript.

Keywords: “Fluidc control”

“co-flow and counter-flow methods usually cooperate with Coanda surface, which has obvious hysteresis”: briefly explain what is the Coanda surface, mentioning curvature, etc. Also, the “obvious” term needs to be explained well by the references, and it is not clear which one of the three listed makes this argument.

The whole Introduction would benefit from a figure showing the different types of mechanisms in a schematic form. As currently written, the section has too many acronyms.

“the most direct and simplest FTV method in engineering”: the statement is too broad, and, again, Ref 16 may not be putting things so strongly.

More information is needed about the “in-house structural grid solver PMB3D”. Equation 1 is unnecessary, and the authors should be commended in not writing a lot of equations that can be found in textbooks, but at least the characteristics of the code, the level of turbulence modeling used, and all the V&V studies (past and/or present) that have been conducted with the code need to be mentioned here. The paper includes a short section of V&V at a later point, but this is the only issue where some more work in needed. The authors mention a grid independence study, but show very brief results (figure 3) with pressure distribution using three different grids. What about the turbulence levels in the nozzle, the parameters used in the models, etc.? These need to be at least touched upon. Figure 3 needs to be expanded to full scale (a sub-image within a sub-image is a first!) and a more sensitive metric than pressure probably needs to be selected. The very brief comments in the text regarding the “inaccurate prediction of Reynolds stress” need to be expanded upon, and a clear connection needs to be made with character of the in-house code and the parameters of the models used. Lastly, a clear statement must be made about the experimental study, results of which are shown in figure 4. Who, what, why, all these need to be clarified here.

 When presenting their CFD results, and discussing the characteristics of different cases of thrust vectoring, the authors should also keep in mind (and discuss!) the possibility that their code is biasing some of the results. For example, the level of recirculation and turbulence is different in different mechanisms, and the results of vector angle and/or efficiency (figure 8) may be sensitive to errors. When the results show small variations (like 1%) the difference may be an artifact of the CFD and not so much a physical result. The authors should not treat their code as a ‘numerical experiment’ DNS, unless of course they are running a DNS, which brings back the previous comment about clarity viz. CFD.

Similar considerations apply to most of the (many) results shown in the (many) figures in the paper. As an example, figure 18 shows a very complex picture, where three recirculation zones interact and create the vectoring effect of the nozzle. Figure 21 shows an even more complex picture with wave reflections and boundary layer/wave interactions. Some critical comments should be included to address the issue of code/model uncertainties and flow physics.  

Articles and prepositions are missing in many places.

Author Response

Please see the attachment

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The issues the Reviewer pointed out in the first revision round were accurately answered. However, using the cold flow in thrust control and nozzle applications is questionable. The flow model is straightforward for any practical application; it can only serve for classical aerodynamic research.