Investigation into the Hydrodynamic Noise Characteristics of Electric Ducted Propeller

Round 1

Reviewer 1 Report

Strengths of paper
1.    Scientific interest is aroused by the results of mathematical modeling of a hydrodynamic noise by FWH equation based on the CFD results.
2.    Simulations were performed using available software and can be used by practicing engineers to optimize the design of a ducted propeller.
3.    The work contains a fairly complete review of the literature, which may be of interest to specialists, researchers, and designers.
Weakness of paper
1.    How the inlet turbulence values have been chosen? 
2.    What is the application of this work? Briefly talk about the result and the implication of the result in the abstract. Please discuss how the findings in this work relate to existing studies in this area. The authors should present the key contribution of this manuscript clearly and illustrate the importance of this study.
3.    In the used test rig, the measuring devices used in the experiment should be described clearly with inserting the accuracy of each one. How many times the experiments are repeated?  How much the error percentage?  What about the standard deviation? Provide the statistical analysis?
4.    Hydrodynamic noise characteristics should be compared with experimental data.

Author Response

Point 1: How the inlet turbulence values have been chosen?

Response 1: Thank you for your suggestion! The inlet turbulence intensity is set to 5% of the initial value in the fluent software.

Point 2: What is the application of this work? Briefly talk about the result and the implication of the result in the abstract. Please discuss how the findings in this work relate to existing studies in this area. The authors should present the key contribution of this manuscript clearly and illustrate the importance of this study.

Response 2: Thank you for your suggestion! The application of this work provides a certain reference for the acoustic performance evaluation and noise reduction optimization of ducted propeller design and the improvement of UUV stealth performance. The original research shows that the sailing speed of the UUV has a great influence on the noise characteristics of the propeller, but does not analyze the reason for the noise change. Therefore, this study focuses on analyzing the relationship between the energy loss of the wake field of the ducted propeller and the noise, and it is found that the vortex at the tail has a certain contribution to the noise. In this paper, the flow field and the sound field are linked, and the flow-induced noise of the ducted propeller is analyzed, which is closely related to the vortex and potential flow. Provides methods and guidance for practicing engineers to use fluent to optimize the design of ducted propellers.

Point 3: In the used test rig, the measuring devices used in the experiment should be described clearly with inserting the accuracy of each one. How many times the experiments are repeated?  How much the error percentage?  What about the standard deviation? Provide the statistical analysis?

Response 3: Thank you for your suggestion! The open water experiments are processed on the built test rig. The test loop includes a steady flow water tank, a transparent experimental section, a return water tank, a circulating pump, a water inlet pipeline and a water discharge pipeline. The circulating pump can change the flow rate of water in the transparent experimental section, which simulate different navigational speed of the ducted propeller. The ducted propeller is hoisted in the transparent experimental section through a designed fixture, and the motor is supplied with 24V DC power by GWINSTEK GPS-3303. The rotational speed and steering are controlled by PWM regulator, which can read the rotational speed of the ducted propeller through PWM, and its rotational speed measurement accuracy is 0.25%. A six-degree-of-freedom force sensor is placed inside the fixture, and its measurement accuracy is 0.1%. Combined with the NI 6343 acquisition card and the LabView data acquisition program, the thrust of the ducted propeller is measured. A six degree of freedom force sensor is placed inside the fixture to measure the thrust combining with the NI 6343 acquisition card and LabView data acquisition program. The input power of the motor can be measured by the power supply, and the reading error of the DC power supply is 0.01W. Combining with the motor efficiency(88%) provided by the manufacturer, the propulsion efficiency of the ducted propeller can be obtained.

Before the open water experiments, the six-degree-of-freedom force sensor was statically calibrated, and the standard weights were used for three repetitions of loading. Before the open water experiments, the six-degree-of-freedom force sensor was statically calibrated, and the standard weights were used for three repetitions of loading. In the same day, six repeated measurement experiments in open water were carried out at 19 different rotational speeds of the ducted propeller. The same water isolating time was used during the experiment. The zero point is collected before each test to ensure that the test system, testers and test conditions are completely consistent and meet the repeatable measurement conditions.

According to the results of 6 repeated open water experiments, the standard deviations of thrust and power of the ducted propeller are 0.26% and 0.34%. Then, the standard uncertainty of the thrust and power measurement repeatability can be obtained by using the Bessel formula, which are 0.29% and 0.41%.

Point 4: Hydrodynamic noise characteristics should be compared with experimental data.

Response 4: Thank you for your suggestion! We understand that hydrodynamic noise experiments may better quantitatively reveal the hydrodynamic noise characteristics of ducted propeller. However,in the present study, we mainly focused on a rough analysis of the hydrodynamic noise of ducted propeller. And we think that hydrodynamic performance experiments may not be optimal, but should be sufficient to draw a conclusion that the flow field simulation method used is relatively accurate, which indirectly verifies the reliability of the noise simulation results. At the same time, the hydrodynamic noise experiments will be the focus of our next research.

Reviewer 2 Report

Fig. 3 could be improved in quality. Otherwise nice and interesting paper that reads well.

Author Response

Point 1: Fig. 3 could be improved in quality. Otherwise nice and interesting paper that reads well.

Response 1: Thank you for your suggestion! Fig. 3 has been replaced in the paper.