Influence of Stern Rudder Type on Flow Noise of Underwater Vehicles

Round 1

Reviewer 1 Report

This is a good thorough work.

 

My remarks are:

·         The FWH model has been developed particularly in view of CAA where M is very high as opposed to flow in water. Therefore, it can be expected that radiated noise from turbulent flow has a very low level. It would be interesting to see absolute values for full scale somewhere, either from full scale investigation or by conversion from model to full scale. Do the authors see a chance to furnish such information?

·         Line 115 kn rather than kN

·         Figures with level graphs: It could be considered to express them with a log frequency scale. It could then be seen more easily that the slope of the spectrum drops at -12 dB/octave for constant absolute bandwidth

·         Figure 6: there is a decibel scale. What is the meaning? Is there a reference value? What is the bandwidth? It is just some ratio with open reference value? A line for explanation would be helpful

·         Figure 6: reference is made to far field prediction and measurement. How has the conversion from a tunnel test to far field been done? Where are reference points A and B

·         Figure 6: the difference between the green and black curve is enormous (60 dB!). Is it possible to elaborate on the reason?

·         Figure 8 to 10: a submarine with a sail generates a strong “collar vortex” on either side of the sail with rotation inwards over the top when seen from behind. This does not really show in the plots. It is rather the separated wake of the sail. It does not become really clear what the effect on flow on the control surfaces may be

·         Further the vortices generated by the sail tend to accelerate flow in the top position, and maybe this is the reason for higher levels of the upper control surfaces. It could be helpful to plot the axial flow in a plane in front of the rudders. Insofar the conclusion 3 seems a bit speculative. I would expect that the highest effect of the + rudder configuration is due to overspeed rather than general turbulent floe or sail vortex shedding

·         Figure 12: as expected the turbulent boundary layer on the surface radiates like a dipole, i.e., in a preferred direction vertical to the surface which is demonstrated nicely in the figure. But the same would be true for the control surfaces

·         Line 267: What is the reason for the low frequency levels? Flow noise tends to be dominated by low frequencies in general. What could be the mechanism for the sail to radiate 20 dB higher levels?

·         As already indicated at the top it could be helpful to calculate absolute levels and full scale to show that this flow noise contribution is important for radiated noise of an underwater vehicle

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Dear authors,

The paper is a good piece of work and its conclusion would be interesting for other researches. In any case, I would advise about some issues in order to improve the quality of the manuscript.

Question 1: The introduction is clear and all the objectives well stated. At the same time, it would be beneficial for the reader if authors include an extended previous literature review to have a complete picture of the state-of-art.

Question 2: The paper can be improved in terms of analytical model. Explain a little bit more in details what are the advantages/disadvantages of your proposal.

Question 3: Please highlight the limitations of your proposal.

Question 4: Future improvements/works could have been more discussed. Please increase this point.

 

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

The present manuscript aims to analyze the sound pressure levels of underwater vehicles with three full appendages having cross-type rudders, X-type rudders, and T-type rudders are compared. The validity of the proposed model and the existence of the sail was examined. The manuscript is fully well written and the quality is completely acceptable. In sum, in this sense, I recommend this manuscript for publishing after a short revision.

1- The abstract is better to modify in terms of narration and most reconsidered. It is better to add more keywords to the paper to be more detectable.

2- It is better to update the references in the introduction. Please focus more on the new publication frequency analysis and LES and Sauer cavitation models, e.g., https://doi.org/10.1016/j.oceaneng.2019.04.070; https://doi.org/10.1016/j.apor.2022.103079; Cavitating Flow Structure and Noise Suppression Analysis of a Hydrofoil with Wavy Leading Edges; https://doi.org/10.1115/1.4053847.

3- In the sentence “the 114 speed of the underwater vehicle is normally in the range of 2 kN-12 kN.” Please change the unit to the SI system.

4- In Eq. 1 & 2, the density for the multiphase flow and the cavitation term must be added. Also, why the author used the WMLES and explained about the SGS used models.

5- “The geometric size of the vehicle is shown in Fig. 1” please add the size to figure 1 (3.2 and 0.4 m). Also, in Fig. 2, please homogenize all variables and bring them based on the maximum length.

Author Response

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Author Response File: Author Response.pdf