Effects of Trailing Edge Deflections Driven by Shape Memory Alloy Actuators on the Transonic Aerodynamic Characteristics of a Super Critical Airfoil

Round 1

Reviewer 1 Report

The scientific and technological significance of this report is admitted in the experimental results of transonic wind tunnel tests. I regret to say that present paper cannot be recommended to the publication.

The principal subject is the mechanical design of morphing wing; however, readers may not be able to figure out the novelty of the mechanism of morphing in this experiment; detailed description should be given.

Next, the chapter 2 “Mechanic modelling and test of shape …” should be revised totally.  In principle, the volume fraction z cannot be mixed up with xA and zM.

Third, figures should be prepared carefully in standard format; see recently published papers in the journal.

Author Response

Thank you for your very helpful comments.

The mechanism of morphing of this paper is explained in more detail.

The nonstandard pictures have been replaced.

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper presents a model for a variable geometry airfoil actuated by SMA wires. There is a comprehensive background presented and the authors compare simulations with measurements in a windtunnel. 

The text is comprehensible but could benefit from a third party with a better domain of the english language. There are eve small typos that should have been detected by a simple spellcheck like line 92 where obtain is spelled "otained", ad four lines before it says "train" instead of strain. 

In general the text used in the figures is too small and difficult to read, that should be corrected

Contentwise, the only thing that I would remoned the authors add to the text is a small discussion on how the structure and the model will be affected as the stress-strain characteristics of the SMA degrade as a result of repeated cycling

Author Response

Thank you for your very helpful comments.

The unclear pictures and small typos have been replaced or corrected.

It has been added to the text about how the stress-strain characteristics of shape memory alloys will be affected by the structure and model when they are recycled.

Reviewer 3 Report

The authors mention a "super critical" airfoil again and again, but do not say which one? There are many supercritical (note proper nomenclature) airfoils. The precise profile is important to name explicitly. This reviewer understands that the airfoil deformed once loaded, but the unloaded profile is critical to know.

There are many small grammatical errors all over the paper. The authors are encouraged to contract a technical native English speaker for rhetorical editing.

Please correct the notation with respect to Mach number. "Ma" is not standard. Please make a proper substitution. Either "M" or "Mach" are standard nomenclature.

Figures 1 - 5 have good trends, but the font sizes are too small to be legible. The axes are also incomplete. Axes on professional journal articles must include:

       Variable Name, Symbol (units)

in that order. Please bring all plots up to proper professional journal standards. This reviewer realizes that many reviewers are lax on this, but such laxity degrades journal quality. This reviewer will insist upon professionalism in approach and presentation.

Because Reynolds effects are clearly coming into play, the scale is imperative to include. Figures 6, 7, 9, 10, 11 need scales for reference.

Figure 7 is woefully incomplete. It is impossible to see what direction forward lies, the spacing of the lines, materials, electrical shielding, aerodynamic fairing geometry and preload mechanism on the lines.

Figures 8 are illegible. Place the airfoils above each other and bring the figure of each airfoil to full left-right justification to make font readable.

The simplified beam model on p. 6 needs to be introduced to the reader as a static model (understanding that dynamics will certainly come into play in the transonic).

Figure 9 Must be renamed to make it clear to the reader that the airfoil shapes are unloaded.

Section 4.2 is incomplete in its description of the experimental setup. Because the authors chose a finite-span  wing, it is critical to properly describe the complete geometry of the test. There is a finite distance from the wing tip to the ceiling. This must be reported as must all other dimensions. The authors are reminded that the standard for international journal publication is repeatability. If a reader is not able to repeat an experiment from the reported work, then it is not worthy of publication.

Figure 13 must explicitly tell the reader where the leading and trailing edges are. Because the figure is 90 deg. from the orientation shown in Figures 10 and 11, it is not possible to ferret these out from the figure itself.

Figures 14, 15 and Section 4.5.2 are incomplete as the authors only report Mach number. It is imperative that the authors also report dynamic pressure and Reynolds number.

The axes on Figures 15, 16  and 17 must be brought up to journal-quality professional standards and include variable name, symbol (units) as described earlier.

Figures 15, 16, and 17 include data from some section of the wing, but it is not clear where it is taken. Because the wing is a finite-span surface, spanwise position counts as tip-relieving will take place whenever lift is generated. The authors must describe to the reader in words and on the figures cited above what the spanwise stations were that were measured.

Please strike the last sentence of Sect. 4.5.3 as it is meaningless: "Chang of the flow structure and aerodynamics induced by trailing edge deflection was obvious and reasonable."

The Conclusions section is completely inadequate. The authors have clearly worked hard and got some real data. This real data needs to be summarized and presented in the Conclusions section. Describe setup geometry, Mach, Dynamic Pressure, Reynolds Number, lift coefficients, sensitivity to angle of attack at given Mach numbers. These are important numbers. Please conclude hard numbers.

General Comments:

The authors must make it clear that all of the analyses are done for the static loading case. Once dynamic aeroelasticity is included, the results will change wildly. Phenomena like aileron buzz will be present in real, dynamic wings, but the authors should describe to the readership that the inherent hysteretic damping characteristics of SMA will help mitigate these problems if not completely render them null.

The authors are encouraged to research the B-47 and its problems with aeroelastic roll reversal as an example. Some of the observations noted with respect to trailing edge deflection sensitivity to Mach and angle of attack may be alleviated by wing torsional flexibility. Comments on this property should be made to orient the reader.

Finally, the authors are encouraged to note that prescribed and dynamic aerocompliance is the key to semi-active dynamic gust load alleviation. The papers of Vos et al. describing his pressure adaptive honeycomb use trailing edge flexibility as a positive feature to be tailored rather than an adverse property to be mitigated. This is the way of the future -- highlight it.

Author Response

Thank you for your very helpful comments.

The selected supercritical airfoil is NASA sc-0714 (2), which is being supplemented.

The grammatical errors have been corrected.

We have modified it to use M for Mach number.

The unclear figures1-5, 8, 13 and 15-17 have been replaced or corrected.

The scales for reference is given in figure 6,7,9,10,11.

A static model has been emphasized in the simplified beam model.

Figure 9 has been renamed.

The distance from the wing tip to the ceiling. has been reported.

The dynamic pressure and Reynolds number have been reported.

The measuring area pf PSP and location of pressure tap have been described in figure 10 and figure 13.

The last sentence of Sect. 4.5.3: "Chang of the flow structure and aerodynamics induced by trailing edge deflection was obvious and reasonable.” has been struck.

The hard numbers has been summarized in conclusion.

Round 2

Reviewer 1 Report

   I regret to say that this revised version cannot be accepted in scientific journal. Although the topic seems to be out-of-date now, we can think of the significance in structure engineering. I consider the paper should have described more details of the structure aspects of the wing; for example, the dimension of wing in Fig. 6 should be presented enough for readers to calculate the value of the second moment of inertial in the elementary equation of (11). The conditions for the FEM in Fig. 8 are completely missing. The dimensions of SMA wire ligament should be presented and the photograph is more appropriate than the drawing of Fig. 7.

   As a number of researchers, including me, were involved in the DARPA project of smart wing around 2000, the studies related to the topics are well known to us. It seemed to me that the bending of wing by SMA wire ligament was one idea, but the torsional actuator of controlling flap angle in place of oil pressure got more attraction to the DAEPA consortium. As 20 years has passed since the project, the novelty and advantage of the ligament mechanism should be claimed as compared with the torsion actuators.

   First of all, the prediction of the blocking stress generated by SMA wire by constitutive equations, Section 2, was not successful, and the part is difficult for us to read, mostly because the symbols and constants appearing in the equations are not defined and these input values are not indicated. Moreover, Eq.2 is the mixture rule of Young’s modulus E, but it was considered as the coefficient W of the increment of x. It is apparent misunderstanding. The jump in the vertical axis of Fig.1 cannot be allowed. The deformation of 9 mm in Fig. 4 means the NiTi showed 9 % shape memory effect. The fact contradicts to our knowledge.  /EOF

Author Response

Dear reviewer, our reply to your modification opinions is attached.

Author Response File: Author Response.docx