To measure the flow velocity of a fluid without affecting its motion state, a method was proposed based on a polyvinylidene fluoride (PVDF) piezoelectric film sensor. A self-made PVDF piezoelectric sensor placed parallel with the flow direction was used to measure the flow velocity. First, the piezoelectric characteristics of PVDF were obtained theoretically. Next, the relationship between flow velocity and sound pressure was verified numerically. Finally, the relationship between flow velocity and the electrical output of the PVDF piezoelectric film was obtained experimentally. In conclusion, the proposed method was shown to be reliable and effective.

https://www.mdpi.com/1424-8220/19/7/1657/pdf

A Flow Velocity Measurement Method Based on a PVDF Piezoelectric Sensor.

Wall-modeled large-eddy simulation of noise generated by turbulence around an appended axisymmetric body of revolution

Flow noise, part of hydrodynamic noise, significantly impacts the stealth capabilities of submarines. Investigating the noise source location and formation mechanism of flow noise is crucial for enhancing submarine stealth performance. This study uses large eddy simulation to examine the evolution of vortex structure in the SUBOFF submarine. The propagation of far-field noise from dipole and quadrupole noise sources of the SUBOFF is calculated, by rationally constructing a permeable integral surface in conjunction with the Ffowcs-Williams and Hawkings and "Collapsing-Sphere" formulations. The numerical results for both flow and acoustic fields are consistent with experimental data and previous numerical findings. Sail and rudder are the predominant dipole noise sources, due to turbulence effects from vortex shedding. The permeable integral surface effectively captures the quadrupole noise source. The quadrupole noise in the 2 kHz frequency range contributes 17 % to 26 % of the total noise energy. The location of the quadrupole noise source and its generation mechanism is explored, through the evolution of the vortex structure and the Lamb vector amplitude. Approximate scaling laws for far-field dipole and quadrupole noise spectra are given, thus illustrating the general laws in the frequency domain of the far-field noise. 

Mechanistic study of noise source and propagation characteristics of flow noise of a submarine

REMOVED: Investigating the sound power level of a simplified underwater vehicle induced by flow separation

The noise control of flank array sonar is a primary approach to enhance the sonar detection range. During submarine navigation, hydrodynamic noise is the main noise source in the platform region of the flank array sonar, which includes flow noise and flow-induced noise. Therefore, an in-depth investigation of hydrodynamic noise is necessary. In this paper, we firstly take the teardrop submarine as a computational model to validate the computational method. Afterwards, we numerically simulate the flow and flow-induced noise characteristics for the cylindrical shell model, and investigate differences in noise at different detection points along the X, Y, and Z axes. Finally, experiments are conducted to confirm the accuracy of the simulation results. The research findings reveal that, at the same frequency, flow-induced noise exceeds flow noise, and the noise decreases as the distance between the walls of the cylindrical shell increases. The experimental and simulation results are consistent, suggesting that the selected computational method can precisely simulate the submarine’s noise.

Research on Characteristics of Flow Noise and Flow-Induced Noise

Hydrodynamic noise is an important noise source of submarine and underwater vehicles when they are cruising at a high speed.Generally,when the Ma number is low,the hydrodynamic noise is mainly radiated by vibrating elastic structures excited by wall-pressure fluctuations beneath turbulent boundary layers(TBL).In this paper,the progress of researching the frequency-wave number spectrum models and the measurement methods of wall-pressure fluctuations beneath TBL were chiefly introduced.And the calculation of acoustic radiation of elastic structures excited by wall-pressure fluctuations beneath TBL is presented.

A review of progress for hydrodynamic noise of ships

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A review of progress for hydrodynamic noise of ships