Fully Coupled Fluid–Structure Interaction with Heat Transfer Effects in an Adaptive NACA Airfoil

Round 1

Reviewer 1 Report (New Reviewer)

Please see the attachment.

Comments for author File: Comments.pdf

Author Response

We wholeheartedly thank the Reviewer for his/her useful suggestions. With this revised submission, we have duly met every point raised. Please find the new version text according to this.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report (New Reviewer)

The authors have addressed all my comments/suggestions. I found their responses quite satisfactory and the revised version has been much improved. I now recommend the paper for publication

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

First, I would like to congratulate the authors for the very interesting piece of work. The paper presents a numerical study of the interaction of fluid, structure and thermals to a SMA shape-changing NACA airfoil. It is very clear and well written, hence only some minor comments can be found below:

1. a couple of minor spelling/formatting mistakes, line 70 "an one-time", line 87 "The Hooke's Law", line 158 the equation goes beyond the margin, between eq.16 and eq.17 "to propose a metrics".

2. In Fig. 2 I find it confusing that NiTi wire (s phase 1) points to the airfoil and PP/PE airfoil (s phase 2) to the wire

3. When describing the mesh, 16 · 10^3 are the triangular cells, but what is the final cell count including the BL quad elements (if they are quad?) Also some more details on the cell count for the three domains (f, s1 and s2) would be interesting to have. Even a picture could be beneficial here. And it should be stated somewhere that the analysis is 2 dimensional.

4. In equation 16, as written, the LHS is a scalar and the RHS a tensor.

5. In figure 5 the y labels and the captions invert L and D (the description of the figure in lines 180-186 is correct)

6. Adding a nomenclature, on top of the list of acronyms, is always good practice.

Author Response

First, I would like to congratulate the authors for the very interesting piece of work. The paper presents a numerical study of the interaction of fluid, structure and thermals to a SMA shape-changing NACA airfoil. It is very clear and well written,...

Thank you so much for your kind consideration.

.... hence only some minor comments can be found below:

1. a couple of minor spelling/formatting mistakes, line 70 "anone-time", line 87 "The Hooke's Law", line 158 the equation goes beyond the margin, between eq.16 and eq.17 "to propose a metrics".

Corrections have been made.

 

2. In Fig. 2 I find it confusing that NiTi wire (s phase 1) points to the airfoil and PP/PE airfoil (s phase 2) to the wire

Fig. 2 has been corrected.

 

3. When describing the mesh, 16 · 10^3 are the triangular cells, but what is the final cell count including the BL quad elements (if they are quad?) Also some more details on the cell count for the three domains (f, s1 and s2) would be interesting to have. Even a picture could be beneficial here. And it should be stated somewhere that the analysis is 2 dimensional.

The requested information were supplied in Par.2.5.

 

4. In equation 16, as written, the LHS is a scalar and the RHS a tensor.

A correction has been made.

 

5. In figure 5 the y labels and the captions invert L and D (the description of the figure in lines 180-186 is correct)

Now Fig.5 and related discussion are in good order.

 

6. Adding a nomenclature, on top of the list of acronyms, is always good practice.

Unfortunately the Journal template does not provide a format for Nomenclature, therefore at present state, the nomenclature is provided within the text itself.

Reviewer 2 Report

The authors performed a numerical study on the Fully-Coupled Fluid-Structure Interaction with Heat Transfer Effects in an Adaptive NACA Airfoil.

The main results are to be presented in the abstract.

The novelty of the work is to be clearly stated.

The introduction is very short and should be extended.

The used commercial numerical software is to be mentioned in the text.

The used turbulence model is to be justified.

Is it realistic to consider time independent governing equations?

The numerical method is to be detailed.

A figure presenting the used mesh is to be presented.

The results of the grid sensitivity test are to be presented.

What are the dimensions of the computational domain? To be justified.

Are the values of the nominal power feed, realistic ? is it logical to reach 500 K as temperature?

What is the considered value of T0?

A validation/verification of the numerical model is to be performed.

The scientific soundness is relatively low.

It will be interesting to present the streamlines, for a better understanding of the flow structure.

A nomenclature is to be added.

English level needs to be improved.

Author Response

1. The main results are to be presented in the abstract.

Information have been supplemented.

 

2. The novelty of the work is to be clearly stated.

Information have been supplemented.

 

3. The introduction is very short and should be extended.

The introduction has been improved as requested.

 

4. The used commercial numerical software is to be mentioned in the text.

The information has been supplemented.

 

5. The used turbulence model is to be justified.

The information has been supplemented.

 

6. Is it realistic to consider time independent governing equations?

Yes it is, considering the steady-state regime that was assumed (Par. 2.1).

 

7. The numerical method is to be detailed.

Information have been supplemented (Par. 2.5).

 

8. A figure presenting the used mesh is to be presented.

A new Figure 4 has been provided.

 

9. The results of the grid sensitivity test are to be presented.

A new Figure 3 has been provided along with the related discussion.

 

10. What are the dimensions of the computational domain? To be justified.

The information has been supplemented (Par. 2.5).

 

11. Are the values of the nominal power feed, realistic ? is it logical to reach 500 K as temperature? What is the considered value of T0?

Considering the 2-D dimensionality and the maximum level of the power feed (1 kW), the maximum temperature of about 480 K (ca. 200 °C) is quite realistic indeed. T0 was 300 K and now this is acknowledged in Par. 3.1.

 

12. A validation/verification of the numerical model is to be performed.

A new discussion on the validity of the calculations for the airfoil with no power feed has been provided in Par. 3.2.

 

13. The scientific soundness is relatively low.

We respectfully disagree. No experiments nor analytical bases were found in the available literature. We believe that the metric we proposed is a step forward in the comprehension of the SMA technology, as applied to aerodynamic profiles.

 

14. It will be interesting to present the streamlines, for a better understanding of the flow structure.

An isocontour map of pressure p (top), and a qualitative map of streamlines (bottom) in the vicinity of the airfoil, at a free-stream air velocity v₀ = 30 m/s, for the maximum allowable power feed, are reported here per Reviewer's suggestion. It is seen that no additional information is provided for the application at hand, therefore such plots are not included in the revised version.

 

15. A nomenclature is to be added.

Unfortunately the Journal template does not provide a format for Nomenclature, therefore at present state, the nomenclature is provided within the text itself.

 

16. English level needs to be improved.

English language has been reviewed throughout.

Author Response File: Author Response.pdf

Reviewer 3 Report

This work seems like a good first step; however, it is too early in the process. It is primarily a COMSOL model without validation. There are some data presented and it is hard to judge the value of this data. 

Literature Survey

·         The literature survey does not examine in-depth this problem

·         Figure 1 is from another paper – has copyright permission been obtained?

o   The authors reference Sofla et al.[1] but in that paper Sofla et al cite the source as Elzey et al.[2]. I could not find the figure in that paper – so it would be useful to confirm the source.

·         It is also clear from the references provided that the structure of morphing airfoils are complex interconnected structures.  

·         The authors have presented similar work [3]

Materials and Assumptions

·         Section 2 is largely a discussion on setting up a COMSOL model. It is unlikely (and unnecessary) to include the governing equations. References used (see for example 17,19 from authors) do not necessarily mean they are used by COMSOL. It is more appropriate to list the libraries used from COMSOL

Results and Discussions

·         There is no real discussion on the results to show insight

o  For example “evidences that thermal nonuniformity plays a role preventing the desired operation, and should be addressed in the design phase. Indeed, the SMA wire ends appear to be up to 100 K colder than its midsection. In these cases, a traditional non-SMA Joule heating provided in coldest section could even be prescribed, to achieve thermal uniformity and ensure uniform SMA activation” is not discussing the differences between the 5 subfigures

o   This is the discussion on Figure 4. “Five velocity maps are reported, with varying ˙QJ: the maximum velocity is found around 35 m/s over the extrados in the top frame case, when ˙QJ = 1000 W. It is interesting to note that in this case the FSI effect the shape-changed airfoil case appears as slightly flattened out” is insufficient and impossible for the reader. Please note I do not understand what extrados is.

o   This continues with the discussion on Figures 5 and 6

·         This work needs some validation

Conclusions

·         Some of the conclusions (e.g., lines 199-201) are not supported with evidence from the results and discussions.

o   This is the only line remotely linked to this (177-178) “It is interesting to note that in this case the FSI affect the shape-changed airfoil case appears as slightly flattened out” but really the figure is unreadable and uninterpretable.

·         Ultimately, every other morphing airfoil in the literature is not a single piece of SMA – it is a complex interconnecting mechanism. This uses a standard commercial code with limited modification of an overly simplified model.

 

Author Response

1. The literature survey does not examine in-depth this problem

No experiments nor analytical bases were found in the available literature. We believe that the metric we proposed is a step forward in the comprehension of the SMA technology, as applied to TASC profiles.

 

2. Figure 1 is from another paper – has copyright permission been obtained?

Figure 1 is fundamentally different from the one we developed for another paper. Here, an airfoil is depicted, associated for the first time with a SMA wire, to come up to a TASC airfoil configuration.

 

3. The authors reference Sofla et al.[1] but in that paper Sofla et al cite the source as Elzey et al.[2]. I could not find the figure in that paper – so it would be useful to confirm the source.

We thank the Reviewer for coming across this discrepancy. In the Sofla, Meguid, Tan and Yeo paper, this figure is indeed present (Page 1289), but it is referred to a ELZEY, SOFLA and WADLEY paper, that is now rightfully inserted in our bibliography (item 11).

 

4. It is also clear from the references provided that the structure of morphing airfoils are complex interconnected structures.

We fully agree, and we explain in the paper how to come up with a model that is based on this very fact.

 

5. The authors have presented similar work [3]

Here, a TASC airfoil is analysed and solved for the first time, and the related metric is developed.

 

6. Section 2 is largely a discussion on setting up a COMSOL model. It is unlikely (and unnecessary) to include the governing equations. References used (see for example 17,19 from authors) do not necessarily mean they are used by COMSOL. It is more appropriate to list the libraries used from COMSOL.

We respectfully disagree with the Reviewer. We think that the analysis based on the presentation of the governing Equations is paramount to the comprehension of the nature of the intertwined transport phenomena, that result inherently intertwined and interdependent one another.

The libraries used by the model have been now listed in Par. 2.7.

 

7. There is no real discussion on the results to show insight

For example “evidences that thermal nonuniformity plays a role preventing the desired operation, and should be addressed in the design phase. Indeed, the SMA wire ends appear to be up to 100 K colder than its midsection. In these cases, a traditional non-SMA Joule heating provided in coldest section could even be prescribed, to achieve thermal uniformity and ensure uniform SMA activation” is not discussing the differences between the 5 subfigures

This discussion has been reworded to meet the Reviewer's considerations.

 

8. This is the discussion on Figure 4. “Five velocity maps are reported, with varying ˙QJ: the maximum velocity is found around 35 m/s over the extrados in the top frame case, when ˙QJ = 1000 W. It is interesting to note that in this case the FSI effect the shape-changed airfoil case appears as slightly flattened out” is insufficient and impossible for the reader. Please note I do not understand what extrados is.

Extrados = technical term (common in airfoil engineeering) for the airfoil's convex side. Now this comment has been reworded.

 

9. This continues with the discussion on Figures 5 and 6 - This work needs some validation

A validation is now provided in Par. 3.2 with respect to the classic literature on airfoils, but with no power feed. No other experiments nor other analytical bases were found in the available literature. We believe that the metric we proposed is a step forward in the comprehension of the SMA technology, as applied to TASC profiles.

 

10. Some of the conclusions (e.g., lines 199-201) are not supported with evidence from the results and discussions.

This discussion has been reworded to meet the Reviewer's considerations.

 

11. This is the only line remotely linked to this (177-178) “It is interesting to note that in this case the FSI affect the shape-changed airfoil case appears as slightly flattened out” but really the figure is unreadable and uninterpretable.

This discussion has been reworded to meet the Reviewer's considerations.

 

12. Ultimately, every other morphing airfoil in the literature is not a single piece of SMA – it is a complex interconnecting mechanism. This uses a standard commercial code with limited modification of an overly simplified model.

We respectfully disagree with the Reviewer. The system is indeed a complex interconnected "mechanism". The simplifying assumptions have been stated clearly in the paper, and the PDE model has been solved with due rationale, offering for the first time useful insights on how the aerodynamic efficiency depends in a non-trivial way on the power feed.

Round 2

Reviewer 2 Report

The paper has low scientific soundness and without any novelty. The numerical model already exist in the examples library of COMSOL.

Author Response

The paper has low scientific soundness and without any novelty: With all due respect, the Reviewer has got no clue on the application at hand. The bibliographic review revealed already that no such application exist in the available literature: modeling of morphing via thermally-activated SMAs was never studied, as duly reported in the paper. Active morphing is important in the automotive and aerodynamic sectors alike.  

The numerical model already exist in the examples library of COMSOL. This is wrong: with all due respect, the Reviewer has got no clue on the modeling framework. We kindly invite the Reviewer to prove his/her statement, by directing the Editorial office to this alleged example library of COMSOL.

 

 

Reviewer 3 Report

Figure 1 in this manuscript and Figure 4 from (Sofla et al., 2010) are the same – please highlight differences between the two. (Elzey et al., 2005) does not include this figure – I believe Sofla et al. were mistaken in their reference.

The modeling here uses a commercial code and simplifies the required mechanics significantly. There s no experimental validation of the code – and the morphing mechanics have been greatly simplified. I cannot recommend this paper. If the authors provided validation through experimentation or introduced a morphing mechanism similar to that found in other studies, this would provide a basis for a valuable contribution.

Author Response

Figure 1 in this manuscript and Figure 4 from (Sofla et al., 2010) are the same – please highlight differences between the two. (Elzey et al., 2005) does not include this figure – I believe Sofla et al. were mistaken in their reference: Figure 4 does not have anything to do with Sofla et al. - it was produced in our research group, and we hold the original artwork for it. As for Figure 1, we include here a screenshot of the work by Sofla et al. that was referenced in the previous version of the paper. We do not know which version of our paper the Reviewer is talking about: we reviewed our submission by duly pointing at the original paper by Elzey and Sofla: the research group was the same, and our citation is now compliant of the copyright.

The modeling here uses a commercial code and simplifies the required mechanics significantly: to date, no such problem has ever been attacked and solved for aerodynamic profiles. With all due respect, we do not understand this what has to do with employing a commercial code. Maybe the Reviewer thinks that research performed with commercial codes deserves no merit? How much of the current published body of work would remain, in the available literature, if we were to take his/her views? Besides, all simplifications were duly declared: without them, the advancement of technology would be quite unfeasible.

There s no experimental validation of the code – and the morphing mechanics have been greatly simplified. I cannot recommend this paper. If the authors provided validation through experimentation or introduced a morphing mechanism similar to that found in other studies, this would provide a basis for a valuable contribution: there's not experimental validation available for this application, yet, and its inclusion in the present work is out of question: this submission lies within a modeling framework, for which the difficulties have been considerable. Simultaneous solution of structural, thermal and fluid dynamics governing equations; ALE formulation for solving the geometry deformation. We kindly ask the Reviewer to direct the Editorial Office to any papers that address such complicated matter. The mechanism of morphing is simplified but still a realistic one, considering the difficulties and the theoretical challenges solved. We believe that this paper deserves publication (in this respected Journal or elsewhere) as it paves the way for this interesting application of thermally-activated morphing in the aerodynamic framework.