Mechanism of aeroacoustic sound generation and reduction in a flow past oscillating and fixed cylinders

2017 ◽  
Vol 832 ◽  
pp. 241-268 ◽  
Author(s):  
Yuji Hattori ◽  
Ryu Komatsu
Keyword(s):  
Sound Pressure ◽  
Fluid Motion ◽  
Acoustic Power ◽  
Sound Generation ◽  
Oscillating Cylinder ◽  
Displacement Effect ◽  
Penalization Method ◽  
Flow Past ◽  
Volume Penalization Method ◽  
Fixed Cylinder

The aeroacoustic sound generated in a flow past two cylinders, one of which is oscillating and the other is fixed, is studied by direct numerical simulation. This problem involves key ingredients of the aeroacoustic noise generated from wind turbines, helicopters, axial flow fans and other turbomachinery: flow, a moving body and a fixed body. The corrected volume penalization method is successfully applied to resolve the sound pressure of aeroacoustic waves as a solution of the compressible Navier–Stokes equations. The sound pressure was shown to be in good agreement with the prediction by the Ffowcs Williams–Hawkings aeroacoustic analogy, which takes account of the cylinder motion, confirming the accuracy of the corrected volume penalization method. Prior to the case of two cylinders, sound generation in flow past a single oscillating cylinder is considered. The fluid motion can be either periodic or non-periodic depending on the frequency and the amplitude of cylinder oscillation. The acoustic power is significantly reduced when the fluid motion locks in to a frequency lower than the natural frequency of vortex shedding from a fixed cylinder. When a fixed cylinder is added, the acoustic power depends strongly on the distance between the cylinders, since that determines whether synchronization occurs and the phase difference between the three forces: the lift forces exerted on the two cylinders and the inertial force due to volume displacement effect of the oscillating cylinder. In particular, significant sound reduction is observed when the fixed cylinder is placed upstream and the frequency of the cylinder oscillation is set to the frequency for which the acoustic power is minimized in the single-cylinder case.

scholarly journals Supersonic Windtunnel Noise Attenuation

2021 ◽  
Author(s):  
William Wai Lim Wong
Keyword(s):  
Wind Tunnel ◽  
Sound Pressure Level ◽  
Noise Level ◽  
Sound Pressure ◽  
Power Level ◽  
Mesh Size ◽  
Acoustic Power ◽  
Pressure Level ◽  
Supersonic Wind Tunnel ◽  
Acoustic Treatment

The aerodynamic generated noise in the supersonic wind tunnel during operation at Ryerson University has exceeded the threshold of hearing damage. An acoustic silencer was to be designed and added to the wind tunnel to reduce the noise level. The main sources of noise generated from the wind tunnel with the silencer were identified to be located at the convergent divergent nozzle and the turbulent region downstream of the shock wave at the diffuser with the maximum acoustic power level of the entire wind tunnel at 161.09 dB. The designed silencer provided an overall sound pressure level reduction of 21.41 db which was considered as acceptable. Refinement to the mesh size and changes to the geometry of the mixing chamber was suggested for a more accurate result in noise output as well as flow conditions would match up to the physical flow. Additional acoustic treatment should be applied to the wind tunnel to further reduce sound pressure level since the noise level still exceeded the threshold of hearing loss.

THE ENERGETIC COSTS OF CALLING IN THE BUSHCRICKET REQUENA VERTICALIS (ORTHOPTERA: TETTIGONIIDAE: LISTROSCELIDINAE)

1993 ◽  
Vol 178 (1) ◽  
pp. 21-37 ◽  
Author(s):  
W. J. Bailey ◽  
P. C. Withers ◽  
M. Endersby ◽  
K. Gaull
Keyword(s):  
Body Mass ◽  
Sound Pressure ◽  
Metabolic Cost ◽  
Acoustic Power ◽  
Metabolic Energy ◽  
Energetic Cost ◽  
Metabolic Efficiency ◽  
Metabolic Costs ◽  
Sound Pressure Levels ◽  
The Relationship

1. The metabolic costs of calling for male Requena verticalis Walker (Tettigoniidae: Listroscelidinae) were measured by direct recordings of oxygen consumption. The acoustic power output was measured by sound pressure levels around the calling bushcricket. 2. The average metabolic cost of calling was 0.143 ml g-1 h-1 but depended on calling rate. The net metabolic cost of calling per unit call, the syllable, was calculated to be 4.34×10-6+/−8.3×10-7 ml O2 syllable-1 g-1 body mass (s.e.) from the slope of the relationship between total V(dot)O2 and rate of syllable production. The resting V(dot)O2, calculated as the intercept of the relationship, was 0.248 ml O2 g-1 body mass h-1. 3. The energetic cost of calling for R. verticalis (average mass 0.37 g) was estimated at 31.85×10-6 J syllable-1. 4. Sound pressure levels were measured around calling insects. The surface area of a sphere of uniform sound pressure level [83 dB SPL root mean square (RMS) acoustic power] obtained by these measurements was used to calculate acoustic power. This was 0.20 mW. 5. The metabolic efficiency of calling, based on total metabolic energy utilisation, was 6.4 %. However, we propose that the mechanical efficiency for acoustic transmission is closer to 57 %, since only about 10 % of muscle metabolic energy is apparently available for sound production. 6. R. verticalis emits chirps formed of several syllables within which are discrete sound pulses. Wing stroke rates, when the insect is calling at its maximal rate, were approximately 583 min-1. This is slow compared to the rates observed in conehead tettigoniids, the only other group of bushcrickets where metabolic costs have been measured. The thoracic temperatures of males that had been calling for 5 min were not significantly different from those of non-calling males. 7. For R. verticalis, calling with relatively slow syllable rates may reduce the total cost of calling, and this may be a compensatory mechanism for their other high energetic cost of mating (a large spermatophylax).

scholarly journals Development of Direct-Vibration Actuator for Bezel-Less Display Panels on Mobile Phones

2020 ◽  
Vol 10 (14) ◽  
pp. 4975 ◽  
Author(s):  
Ki-Hong Park ◽  
Zhi-Xiong Jiang ◽  
Yuan-Wu Jiang ◽  
Sang-Moon Hwang
Keyword(s):  
Mobile Phones ◽  
Sound Pressure ◽  
Wearable Devices ◽  
Pressure Level ◽  
Sound Generation ◽  
Force Factor ◽  
Display Design ◽  
3D Finite Element ◽  
3D Finite Element Method ◽  
Direct Vibration

With the development of technology, multimedia devices such as smartphones, tablets, and wearable devices have become necessities in our lives, and many new products are introduced every year. Companies are expanding smartphone displays and are developing bezel-less display panel designs. The enlarged display limits the space available for a speaker, and a new actuator must therefore be developed. Indirect-vibration actuators were developed for full-wide display designs. Using the same sound-generation principle as that of the indirect-vibration actuator, the mechanism and design of the direct-vibrating actuator is proposed in this paper. Using 3D finite element method (FEM), the force factor is obtained and used for design optimization. A sample is produced, and an experiment is conducted for sound pressure level (SPL) comparison. The experiment results show that the newly designed direct-vibration actuator can replace the dynamic receiver in mobile devices and enable the application of the bezel-less display design.

Coupling Between Acoustic Resonance and Fluidelastic Instability in Normal Triangular Tube Arrays

2006 ◽  
Author(s):  
John Mahon ◽  
Craig Meskell
Keyword(s):  
Flow Velocity ◽  
Sound Pressure ◽  
Physical Mechanism ◽  
Acoustic Resonance ◽  
Acoustic Power ◽  
Structural Damping ◽  
Duct Acoustics ◽  
Tube Arrays ◽  
Fluidelastic Instability ◽  
Independent Parameters

This paper reports on the interaction between fluidelastic instability (FEI) and acoustic resonance. In order to examine the interaction, the duct acoustics were excited with speakers placed adjacent to the tube array to artificially replicate flow-induced acoustic resonance. While the current study has clearly captured the phenomenon of interaction between the fluidelastic motion at ∼ 10 Hz and the acoustic field at ∼ 1kHz, it is not apparent what the physical mechanism at work might be. The paper details the effect on RMS level of tube vibration for three independent parameters: flow velocity, structural damping and acoustic power. The results presented show that there is a corresponding fall in the FEI vibration amplitude with increasing sound pressure level in the tube array. In addition, the effects of flow velocity and structural damping in conjunction with forced acoustics on the RMS of tube displacement are discussed.

Low-dimensional modelling of sound generation by a flow past a bluff body

2012 ◽  
Vol 131 (4) ◽  
pp. 3428-3428
Author(s):  
K. H. Seid ◽  
Randolph C. K. Leung ◽  
Garret C. Y. Lam
Keyword(s):  
Bluff Body ◽  
Sound Generation ◽  
Flow Past ◽  
Low Dimensional

Fluid mechanics and sound generation for lung-clearance therapy

2017 ◽  
Vol 27 (4) ◽  
pp. 820-838
Author(s):  
John Gorman ◽  
Eph Sparrow ◽  
Kevin Krautbauer
Keyword(s):  
Fluid Flow ◽  
Fluid Mechanics ◽  
Design Methodology ◽  
Complete System ◽  
Fluid Velocity ◽  
Fluid Motion ◽  
Sound Generation ◽  
Content Type ◽  
Primary Means ◽  
Therapeutic Device

Purpose The study described here aims to set forth an analysis approach for a specific biomedical therapeutic device principally involving fluid mechanics and resulting sound generation. The function of the therapeutic device is to clear mucus from the airways of the lungs. Clearance of the airways is a primary means of relief for cystic fibrosis and is also effective in less profound dysfunctions such as asthma. The complete system consists of a device to periodically pulse air pressure and a vest that girdles the abdomen of the patient and receives and discharges the pulsating airflow. The source of pulsed air can be tuned both with respect to the amplitude and frequency of the pressure pulsations. Design/methodology/approach The key design tools used here are computational fluid dynamics and the theory of turbulence-based sound generation. The fluid flow inside of the device is multidimensional, unsteady and turbulent. Findings Results provided by the fluid mechanic study include the rates of fluid flow between the device and the inflatable vest, the rates of air supplied to and extracted from the device, the fluid velocity magnitudes and directions that result from the geometry of the device and the magnitude of the turbulence generated by the fluid motion and the rotating component of the device. Both the velocity magnitudes and the strength of the turbulence contribute to the quantitative evaluation of the sound generation. Originality/value A comprehensive literature search on this type of therapeutic device to clear mucus from the airways of the lungs revealed no previous analysis of the fluid flow and sound generation inside of the device producing the pulsed airflow. The results presented in this paper pinpoint the locations and causes of sound generation that can cause audible discomfort for patients.

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