Aerodynamic Damping Prediction for Turbomachinery Based on Fluid-Structure Interaction with Modal Excitation
Round 1
Reviewer 1 Report
- Provide the details of the temporal discretization used for the structural problem. There should be options in both ANSYS and CFX to specify/obtain information about this. This is very important for this paper because the results of the vibrational problem, especially the coupled problem, depending significantly on the time solver used for each.
- Additionally, no information is given about convergence criteria for either structure or fluid, time-step size for either material, convergence criteria for overall system. This information should be provided with each numerical example, such that the reader could reproduce the results of the examples.
- The introduction is a bit ambiguous with the nomenclature: “coupled”. Coupled could mean one-way or two-way coupled; and partitioned evolution or monolithic evolution. For example, the approach followed in the paper is a two-way coupled, partitioned FSI method.
- Equation (6): why is thermal flow coupled here? Are you solving the thermal equations in the solid? How is the thermal flow evaluated in the compressible fluid? Is the structural constitutive equation dependent on temperature? Is there an advection-diffusion solved in the fluid? If it’s not relevant, remove it from the coupling conditions.
- Figure 9: the vertical axes limits should be the same for both plots.
- For example: “modal response in vacuum”, is it unexpected that the first mode results in smaller displacements than the second mode? I thought this was not usually the case – perhaps you could comment on this.
- Figure 20: Why are there points every Force/N = 0.05 up to 0.25, then no points until 0.5? The behavior of the design point and flutter point curves shows a significant instability at 0.5, but is that gradual or abrupt near 0.5? Also what if the 0.5 value is less converged, and the behavior is actually stable at points 0.3, 0.4, … More points should be evaluated here before a conclusion is drawn from the response (e.g. “this phenomenon demonstrates that the nonlinear vibration has significant effect on the aeroelastic stability”.
- The statement “However, the aerodynamic damping transits from positive to negative presenting the blade tends to be instability” needs to be clarified and rewritten – is there a “with increasing force amplitude” missing? Again, I do not think you can draw this conclusion unless the high excitation force points are investigated further.
- The details of the study of IBPA come across as a last-minute toss-in to the paper, and neither the analysis, investigation, or conclusion are complete. For example, you only ran one additional case at phase angle 180 degrees; why not choose 15, 30, 45? Because 180 has an obvious implication of mirroring and boundary condition effects. Simply running quickly one different value of phase angle and not doing any kind of sensitivity study or further details does not warrant any sound conclusion: “applicability of this method for dealing with the non-zero IBPA has also been illustrated” – I would say not really, and I’m not confident that either a) results can be trusted, or b) we have any additional understanding of the response of non-zero IBPA than before reading this paper.
- Conclusion: “novel prediction method for aerodynamic damping … logarithmic decrement theory”: You may expand on this statement, because logarithmic and exponentially decaying functions have been used in damping problems many times in other studies, including aerodynamic damping models (e.g. see: “Numerical study on aerodynamic damping of floating vertical axis wind turbines Cheng, Zhengshun; Aagaard Madsen , Helge; Gao, Zhen; Moan, Torgeir Published in: Journal of Physics: Conference Series (Online) Link to article, DOI: 10.1088/1742-6596/753/10/102001 Publication date: 2016” and “https://brilliant.org/wiki/deriving-exponential-decay-from-damping-forces/”). I do think there is something novel here, but it’s not the reader’s job to discern what that is, rather the author’s job to concisely convey what is novel.
Author Response
Dear reviewer:
I am very grateful to your comments for the manuscript. According with your advice, we amended the relevant part in manuscript using the 'Track Changes'. And a document answering every question from the referees is also summarized and enclosed.
Please see the attachment. Should you have any questions, please contact us without hesitate.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The authors propose a method for predicting aerodynamic damping for turbomachinery applications based on FSI simulations. Although the damping prediction based on logarithmic decrement theory is not entirely new, the paper is well written and may be of interest to readers. Therefore, I suggest to accept the paper for publication.
In order to improve the quality of the publication, some points should be addressed:
A more detailed discussion of the computational method used in the study (numerical details, structure, etc.).
Moderate editing of the language is required.
Author Response
Dear reviewer:
I am very grateful to your comments for the manuscript. According with your advice, we amended the relevant part in manuscript using the 'Track Changes'. And a document answering every question from the referees is also summarized and enclosed.
Please see the attachment. Should you have any questions, please contact us without hesitate.
Author Response File: Author Response.pdf
Reviewer 3 Report
Dear authors,
Please find attached my review report.
Regards
Comments for author File: Comments.pdf
Author Response
Dear reviewer:
I am very grateful to your comments for the manuscript. According with your advice, we amended the relevant part in manuscript using the 'Track Changes'. And a document answering every question from the referees is also summarized and enclosed.
Please see the attachment. Should you have any questions, please contact us without hesitate.
Author Response File: Author Response.pdf
