A Model to Predict Acoustic Resonant Frequencies of Distributed Helmholtz Resonators on Gas Turbine Engines
Round 1
Reviewer 1 Report
The authors present a methodology for predicting the resonance frequencies of distributed Helmholtz resonators. The methodology is based on deriving a simulation model, which is later on validated by means of measurements.
The paper is very well written with the scope being clearly stated in the introduction. The latter is put together in a descriptive manner thus, listing what is being research so far in regards to distributed Helmholtz resonators.
The theoretical model is adequately described and the acompanied test process is well outlined.
Some minor comments:
Referencing seems not to be working, i.e.an error occurs while linking the references into the text.
Minor typo correctios required mainly due to the extensive use of commas as well as missing space between some words.
Did the author conduct a convergence study related to the element size of the CFD model? Please provide, if yes.
p. 15, l.339-343: what is the reason for the observed deviation? Have you tried adapting your CFD model to minimize the discrepancies?
What are the CFD assumptions that, if changed, could give a better discrepancy ratio related to the measured results?
Author Response
The authors present a methodology for predicting the resonance frequencies of distributed Helmholtz resonators. The methodology is based on deriving a simulation model, which is later on validated by means of measurements.
The paper is very well written with the scope being clearly stated in the introduction. The latter is put together in a descriptive manner thus, listing what is being research so far in regards to distributed Helmholtz resonators.
The theoretical model is adequately described and the accompanied test process is well outlined.
The author would like to thank the reviewer for your valuable advice and the recognition of the quality of this work.
Some minor comments:
Referencing seems not to be working, i.e.an error occurs while linking the references into the text.
Re: Cross references are all fixed.
Minor typo corrections required mainly due to the extensive use of commas as well as missing space between some words.
Re: Thank you very much for pointing this out and excuse us for the carelessness. A few editing problems have been added where they should be, such as space are added in line 124 between “h” and “is”, and in line 175 between “4” and “is”, et.c.
Did the author conduct a convergence study related to the element size of the CFD model? Please provide, if yes.
Re: The reviewer pointed out a very critical point when using CFD as a research tool. The author did notice the importance of a mesh independence study. The result is given in Section 2.1 in the revised manuscript. In Figure.6, an even finer element size produces very close result with the element size being used in the paper. Therefore, the current mesh size is proved to be sufficiently fine enough to get mesh independent results.
p. 15, l.339-343: what is the reason for the observed deviation? Have you tried adapting your CFD model to minimize the discrepancies?
Re: The CFD method in this paper is kept constant which is using the same unsteady compressible laminar flow solver. The time step and element size are both identical throughout the paper as well. The empirical model is acquired by careful mathematical regression practice and it turned out that the CFD results meet the proposed model very closely with little deviation.
What are the CFD assumptions that, if changed, could give a better discrepancy ratio related to the measured results?
Re: The propagation of an acoustic plane wave in an impedance tube, incident normal to a perforated plate is resolved as an unsteady compressible laminar flow with satisfactory temporal and spatial resolution in this work. Simulation of such flow regimes do not require significant modelling approximations such as turbulence modeling and any significant geometry simplifications. Therefore, to the author’s knowledge, in the context of this application, CFD modelling may be considered to be a direct numerical solution of the governing Navier-Stokes equations and is thus not a major source of error. The discrepancy between the model and experimental result in Figure. 18 should be mainly due to differences in which degree the hole to wall effects take place.
Reviewer 2 Report
The paper provides the reader with a comprehensive analysis on distributed Helmholtz resonators focusing on hole-to-hole interaction effects. The authors face the problem by proposing a CFD model of several perforated plates, from which a simplified model is extracted. They support the approach by comparing numerical and experimental data.
The paper is interesting, and the whole approach is sound.
There are minor issues to be faced, which can be easily solved by a deep proofreading of the document.
First of all, check Figure references along the text. 90% of cross-references are broken (“Error! 100 Reference source not found.”)
· Line 74. Check the sentence. Something is odd
· Line 115. Separate “h” from “is”
· Line 128. “r” should be italic
· Line 162. Separate “4” from “is”
· Eq. 12. Please, use SI unit to express volume
· Line 205. Number of Figure is missing
· Figure 7. It would have been nice to have an additional view of the rig showing the position of four loudspeakers with respect to the cross-section
· Figure 13(a). Why a single orifice is represented? It would be better to show all holes, even though there is no acoustic interaction between them
· Line 315. Check the sentence. Reference to figure numbers are missing
· Line 321. “An even” rather than “A even”
· Line 331. Check the sentence. Figure number is missing
Author Response
The paper provides the reader with a comprehensive analysis on distributed Helmholtz resonators focusing on hole-to-hole interaction effects. The authors face the problem by proposing a CFD model of several perforated plates, from which a simplified model is extracted. They support the approach by comparing numerical and experimental data.
The paper is interesting, and the whole approach is sound.
There are minor issues to be faced, which can be easily solved by a deep proofreading of the document.
The author would like to thank the reviewer for your valuable advice and the recognition of the quality of this work.
First of all, check Figure references along the text. 90% of cross-references are broken (“Error! 100 Reference source not found.”)
· Line 74. Check the sentence. Something is odd
· Line 115. Separate “h” from “is”
· Line 128. “r” should be italic
· Line 162. Separate “4” from “is”
· Eq. 12. Please, use SI unit to express volume
· Line 205. Number of Figure is missing
Re: All above errors have been carefully corrected. All cross references are fixed as well.
· Figure 7. It would have been nice to have an additional view of the rig showing the position of four loudspeakers with respect to the cross-section
Re: Figure 7. Is renewed so that position of those four loudspeakers with respect to the cross section are shown clearly in the new Figure.7.
· Figure 13(a). Why a single orifice is represented? It would be better to show all holes, even though there is no acoustic interaction between them
Re: Figure 13(a) is intended to be a close-up look into the Figure 12 (a) which showed the very little interactions between holes. Similarly Figure 13(b) is a close-up look into Figure12(b).
· Line 315. Check the sentence. Reference to figure numbers are missing
Re: corrected.
· Line 321. “An even” rather than “A even”
Re: corrected.
· Line 331. Check the sentence. Figure number is missing
Re: corrected.
