A Numerical Investigation of Supercavitation Vehicle’s Hydrodynamic Noise

Round 1

Reviewer 1 Report (Previous Reviewer 2)

Comments and Suggestions for Authors The paper has been improved considerably. I understand one of the targets of the research was to demonstrate the effects of different operating conditions and with or without ventilation. The reference location for the sound spectrum is a point on the surface of the cavitator. What can just be judged are differences, in so far a reference value for sound would not be required as it is not intended to indicate the absolute level at 1 m distance which should not be a problem to calculate even if the calculation domain is smaller. I find it problematic to reference research which is classified, therefore reference to that should be minimized. As a minimum, the consideration of the effect of the hydrofoil figure 3 should be cancelled as it does not contribute to the findings discussed later. In total there is no verification or validation of the results which is unsatisfactory as to the reliability of the simulation. Modelling of ventilation is still unclear. Is the direction of the efflux radial or in downstream direction? I would expect a large difference in noise from ventilation. How can one see from Figure 14 that there is dipole characteristics? Fig 13 to 15 numbers on axes still not readable. Consider changing the color of text on red background from black to white. In the FWH formulation please explain S, L, Ω, a0 Comments on the Quality of English Language

Moderate English changes required

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report (New Reviewer)

Comments and Suggestions for Authors

The paper investigates the hydrodynamic noise of a supercavitating vehicle. The Schnerr-Sauer cavitation model is adopted. This is based, on the simplified Rayleigh-Plesset eq. Ffowcs-Williams-Hawkings (HW-H) equations to model noise generation by a conical-headed vehicle operating in the ventilated supercavitating condition and producing noise in a wide (100Hz-100kHz) band. This is claimed to be the novelty of the  manuscript.

I would expect some more information and discussion regarding the selection of the above models, the range of their applicability and the effect of venilation flow on the frequency of noise.

Comments on the Quality of English Language

Minor editing errors.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report (Previous Reviewer 2)

Comments and Suggestions for Authors the manuscript is ok now Comments on the Quality of English Language

Moderate editing of English language

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

Comments and Suggestions for Authors

Reviewer Comments

This paper deals with the cavitation phenomenon and hydrodynamic noise and simulates  the flow field and acoustic field around an underwater supercavitation vehicle under various conditions. Regarding the ventilation cavitation phenomenon, the simulation shows that the low vehicle  speed could reduce the cavitation inception threshold and the high background pressure could  enhance the stability of the supercavitation structure. As for hydrodynamic noise, the simulation  results reveal that when cavitation occurs, the noise spectrum exhibits several characteristic peaks  near 1 kHz and between 3 and 10 kHz. However, the followings should be carefully addressed in the revision to be published in JMSE.

1-      The novelty of the work must be clearly addressed and discussed, compare your research with existing research findings and highlight novelty, (compare your work with existing research findings and highlight novelty).

2-      The authors should be followed the instruction of the journal in all parts and sections in this manuscript. Also, similarity index must be reduced to not more than 20% with not more than 3% from a source. Please check the number of each section, equation, and chart.

3-      Complete mathematic calculation model with all nomenclature missing

4-      The abstract needs more quantitative results. The abstract section is an important and powerful representation of the research. It is better that the results should be presented with the support of specified data.

5-      The main objective of the work must be written on the more clear and more concise way at the end of introduction section,

6-      Introduction section must be written on more quality way, i.e. more up-to-date references addressed. Research gap should be delivered on more clear way with directed necessity for the conducted research work,

7-      The authors should indicate this technique to enhance system performance. Also, the author should add more references that discuss the effect of using this technique. It is recommended that the authors carry out wide analysis and comparison with the state-of-the-art studies.

8-      Most tables and figures are needed improve the quality of all tables and figures.

9-      Add references for all equations.

10-  I would also expect to validate with two more experimental works available in the literature.

11-  The literature review must be improved. Please highlight in the literature review the differences between previous papers and your paper. Please clearly indicate the knowledge gap and prove that it is a really not analyzed area of the field. Please indicate new approach / new methods in a comparison to the existing investigations (literature review should be extended and add below references). Numerical Investigations of Transient Flow Characteristic in Axial Flow Pump and Pressure Fluctuation Analysis Based on the CFD Technique..Numerical investigation of flow field behaviour and pressure fluctuations within an axial flow pump under transient flow pattern based on CFD analysis method.

12-  Description of Acoustic Modelanalysis should be improved.

13-  You need to add error analysis of your results and add the error bars in your graphs to indicate your accuracy measurements.

14-  Improve work justification. Also, add more analysis about velocity and pressure contours.

15-  More quantitative conclusions should be presented. Please prepare additional comparisons, some percentage differences. There is a lack of quantitative conclusions which should contain main findings from the paper and highlight the new and high novelty and contribution of your work to the field.

16-  Present the mathematical equation of the boundary conditions and initial condition.

17-  Conclusion section is missing some perspective related to the future research work, quantify main research findings.

18-  The conclusion section on lacks in summative conclusions. The main results, novelty and academic contributions should be emphasized in this section. Moreover, are the results obtained in this paper really applicable in other similar researches?

19-  In the discussion development, it is very important to emphasize points of agreement or disagreement between results in this work and others cited in references part of manuscript.

20-  Authors should discuss limitations of the current study and possible improvements for future directions/research works. Authors are requested to check the reference format and correct some inconsistent formats.

21-  English language should be carefully checked and carefully check paper for language typos.

22-  Any authorship changes will need to have a specific, valid reason for the update that will be evaluated by the Editor according to journal defining authorship guidelines.

 

 

 

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

 

The paper reports on numerical calculations of a supercavitating vehicle and discusses acoustic implications.

Note that reference to figures is mixed up starting from Fig 10. I will refer to the original numbering of the figures itself. Some of the figures are no readable for too small size.

 

General:

The work combines CFD with the FWH model. FWH models monopole sources, dipole sources and quadrupole sources. The only source of monopoles is the cavitation bubble (referred to in this paper as cavitation flow), the dipole is flow over a rigid surface and quadrupole is from free turbulence, typically not an important source.

It is not clear where exactly the FWH surfaces are. In the cavitation area it could be on the body surface of the body (where it could not radiate if there is a bubble around it) and the surface of the bubble (which is not solid but compliant and therefore would also not radiate as a quadrupole). This leaves the monopole part as the main cause of noise. The authors should discuss these components of the FWH model.

The difference between ventilated and not ventilated is unclear. How is the air considered? It says it has a density of 1.18 kg/m³ (and called incompressible, see page 2, l 46) but this would be under atmospheric pressure, in the bubble it would be the pressure of the bubble. In the non-ventialted case the bubble collapses with hardly a trace but with air it would not. This should have a noise reducing effect rather than the opposite.

There is speculation that the air entry jet is the cause of some of the noise. Has this jet been modelled and, if yes, how?

There is reference to “water depth”. What it should be is rather like “diving depth”.

Details:

Eq 1 and 2 should have complete explanation of paraneters and the meaning of each compoenent be addressed.

L 156 should be Fig 5?

L 159 elements rather than meshes?

L 171 show the coordinate system where the distances refer to. The meaning of a noise level at this location needs to e explained. It would be helpful to refer noise levels to 1 m distance as usual in such evaluations

Table 1 There are 3 cases with different parameters. Is there a connection between the 3. It is difficult to understand because several parameters have been changed form case to case.

Table 2 There is suddenly a “cavitation rate”. What is this?

L 202 Figure has no number

Fig 8: Comparing  this to cases 1-3 there is a visible wake. Is this due to the entrained air? If yes this could be a reason for additional noise due to monopole behavior of air bubbles

L 236 define “critical suzpercaviation”

L 287 turbulent boundary layer, where?

L 298 “Therefore,…” This is purely speculative. There cannot be noise from flow impact on a cavitation bubble and no noise on the body-bubble and bubble-water interface, see above

Fig 12 Please explain in more details what is “total…flow part”

L 311 frictional noise: what is this? How does it relate to the FWH model?

L 347 it is unclear how this can be inferred

L 364 ventilation jet: how does it looks like and how has it been modelled?

L 365 speculative

Conclusion: It is difficult to discuss this one-by-one. Much of this is speculative with no verification. In my opinion main noise is coming from volume fluctuations including bubble collapse as typical in propeller cavitation. This is not at all addressed in the paper.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Reviewer Comments

the followings should be carefully addressed in the revision to be published in JMSE.

1-      The abstract still needs more quantitative results.

2-      Add references for all equations.

3-      You need to add error analysis of your results and add the error bars in your graphs to indicate your accuracy measurements.

4-      Improve work justification. Also, add more analysis about velocity and pressure contours.

5-      More quantitative conclusions should be presented.

6-      Conclusion section is missing some perspective related to the future research work, quantify main research findings.

 

 

 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf