Experimental Visualization of Sound Pressure Level and Vibration Around a Soundproof Barrier

2011 ◽  
Author(s):  
Fumio Shimizu ◽  
Kazuhiro Tanaka ◽  
Koji Yamamoto ◽  
Hiroshi Shigefuji
Keyword(s):  
Noise Reduction ◽  
Sound Pressure Level ◽  
Sound Source ◽  
Sound Pressure ◽  
Pressure Level ◽  
Heat Radiation ◽  
Sound Insulation ◽  
Vibration Displacement ◽  
The One ◽  
The Relationship

The noise and vibration control are the one of important issues. A soundproof barrier, which covers a sound source with sound absorbing materials, is very useful for the noise reduction. When large noise and high temperature heat emit from the sound source, we must also consider the heat radiation as well as the noise reduction. The purpose of the present study is to investigate the relationship between sound pressure level and vibration on a soundproof barrier around a sound source. The effect of heat radiation hole on the sound insulation performance of the soundproof barrier is also investigated. The sound pressure level and the vibration displacement were similarly distributed on the surface of the barrier. Therefore, the vibration of the barrier was strongly influenced to the sound pressure level of the transmitted sound.

scholarly journals Noise Reduction Mechanisms of an Airfoil with Trailing Edge Serrations at Low Mach Number

2019 ◽  
Vol 9 (18) ◽  
pp. 3784 ◽  
Author(s):  
Hui Tang ◽  
Yulong Lei ◽  
Yao Fu
Keyword(s):  
Noise Reduction ◽  
Sound Pressure Level ◽  
Sound Source ◽  
Sound Pressure ◽  
Pressure Level ◽  
Source Distribution ◽  
Noise Mitigation ◽  
Trailing Edge ◽  
Trailing Edge Noise ◽  
Trailing Edge Serrations

Trailing-edge serrations have proven to be valid applications of trailing edge noise mitigation for an airfoil, while the physical noise reduction mechanism has not been adequately studied. We performed simulations employing Large-eddy simulation and the Lighthill–Curle method to reveal the variation in the hydrodynamic field and sound source due to the trailing edge serrations. The grid resolution and computational results were validated against experimental data. The simulation results show that: the trailing edge serrations impede the growth of spanwise vortices and promote the development of streamwise vortices near the trailing edge and the wake; the velocity fluctuations in the vertical cross-section of the streamwise direction near the trailing edge are reduced for the serrated airfoil, thereby obviously reducing the strength of the pressure fluctuations near the trailing edge; and the trailing edge serrations decrease the distribution of the sound source near the trailing edge and reduce the local peak value of sound pressure level in a specific frequency range as well as the overall sound pressure level. Moreover, we observed that, in the flow around the NACA0012 airfoil, the location where the strong sound source distribution begins to appear is in good agreement with the location where the separated boundary layer reattaches. It is therefore effective to reduce trailing edge noise by applying serrations on the upstream of the reattachment point.

Noise Reduction Analysis of Electronic Device Cooling Fan With Duct and Its Application Under Variable Working Conditions

2021 ◽  
Author(s):  
Zonghan Sun ◽  
Jie Tian ◽  
Grzegorz Liśkiewicz ◽  
Zhaohui Du ◽  
Hua Ouyang
Keyword(s):  
Noise Reduction ◽  
Working Conditions ◽  
Sound Pressure Level ◽  
Sound Pressure ◽  
Reduction Method ◽  
Axial Flow ◽  
Pressure Level ◽  
Inlet Flow ◽  
Cooling Fan ◽  
Inlet Duct

Abstract A noise reduction method for axial flow fans using a short inlet duct is proposed. The pattern of noise reduction imposed by the short inlet duct on the axial flow cooling fan under variable working conditions was experimentally and numerically examined. A 2-cm inlet duct was found to reduce tonal noise. As the tip Mach number of the fan increased from 0.049 to 0.156, the reduction in the total average sound pressure level at 1 m from the fan increased from 0.8 dB(A) to 4.3 dB(A), and further achieved 4.8 dB(A) when a 1-cm inlet duct was used. The steady computational fluid dynamics (CFD) showed that the inlet duct has little effect on the aerodynamic performance of the fan. The results of the full passage unsteady calculation at the maximum flow rate showed that the duct has a significant influence on the suction vortexes caused by the inlet flow non-uniformity. The suction vortexes move upstream to weaken the interaction with the rotor blades, which significantly reduces the pulsating pressure on the blades. The sound pressure level (SPL) at the blade passing frequency (BPF) contributed by the thrust force was calculated to reduce by 36 dB at a 135° observer angle, reflecting the rectification effect of the duct on the non-uniform inlet flow and the improvement in characteristics of the noise source. The proper orthogonal decomposition (POD) of the static pressure field on the blades verified that the main spatial mode is more uniformly distributed due to the duct, and energy owing to the rotor-inlet interaction decreases. A speed regulation strategy for the cooling fan with short inlet duct is proposed, which provides guidance for the application of this noise reduction method.

Research on the Noise Reduction and Efficiency Increase for Axial Fan with Wave Leading Edge Blades

2020 ◽  
Author(s):  
Bo Li ◽  
Yujing Wu ◽  
Dange Guo ◽  
Dan Luo ◽  
Diangui HUANG
Keyword(s):  
Noise Reduction ◽  
Sound Pressure Level ◽  
Wave Amplitude ◽  
Sound Pressure ◽  
Noise Analysis ◽  
Leading Edge ◽  
Pressure Level ◽  
Wave Number ◽  
Monitoring Point ◽  
Reduction Effect

Abstract This paper imitates the raised structure of the leading edge of the humpback whale fin limbs, designed six bionic blades. The aerodynamic analysis show that: the wave leading edge blade can improve the total pressure efficiency of the axial flow fan, and under off-design conditions, the aerodynamic performance of bionic fan is better than that of prototype fan. The noise analysis shows that: under the condition of constant wave number, increasing wave amplitude can reduce the overall sound pressure level at the monitoring point, in the middle and high frequency range, the sound pressure level of the bionic fan at the monitoring point is significantly lower than that of the prototype fan, and the noise reduction effect increases with the increase of wave amplitude; under the condition of constant wave amplitude, increasing the wave number can reduce the fan noise. At a certain wave number and amplitude, the overall sound pressure level of the bionic fan at the monitoring point is at most 2.91 dB lower than that of the prototype fan. In this paper, the noise reduction effect of increasing wave number is more obvious than that of increasing wave amplitude.

scholarly journals Reducing the harmful effects of noise on the human environment. Sound insulation of industrial skeleton enclosures in the 10–40 kHz frequency range

2020 ◽  
Vol 18 (2) ◽  
pp. 1451-1463
Author(s):  
Witold Mikulski
Keyword(s):  
Sound Pressure Level ◽  
Sound Pressure ◽  
Sheet Steel ◽  
Pressure Level ◽  
Sound Insulation ◽  
Frequency Range ◽  
Noise Sources ◽  
Human Environment ◽  
Absorbing Material ◽  
Acoustic Enclosures

Abstract Purpose The purpose of the research is to work out a method for determining the sound insulation of acoustic enclosures for industrial sources emitting noise in the frequency range of 10–40 kHz and apply the method to measure the sound insulation of acoustic enclosures build of different materials. Methods The method is developed by appropriate adaptation of techniques applicable currently for sound frequencies of up to 10 kHz. The sound insulation of example enclosures is determined with the use of this newly developed method. Results The research results indicate that enclosures (made of polycarbonate, plexiglass, sheet aluminium, sheet steel, plywood, and composite materials) enable reducing the sound pressure level in the environment for the frequency of 10 kHz by 19–25 dB with the reduction increasing to 40–48 dB for the frequency of 40 Hz. The sound insulation of acoustic enclosures with a sound-absorbing material inside reaches about 38 dB for the frequency of 10 kHz and about 63 dB for the frequency of 40 kHz. Conclusion Some pieces of equipment installed in the work environment are sources of noise emitted in the 10–40 kHz frequency range with the intensity which can be high enough to be harmful to humans. The most effective technical reduction of the associated risks are acoustic enclosures for such noise sources. The sound pressure level reduction obtained after provision of an enclosure depends on its design (shape, size, material, and thickness of walls) and the noise source frequency spectrum. Realistically available noise reduction values may exceed 60 dB.

Loudness of Structure-Borne Sound Heard Directly by Ear Put on Vibrating Structure

2003 ◽  
Vol 22 (1) ◽  
pp. 27-32
Author(s):  
Takuya Fujimoto
Keyword(s):  
Sound Pressure Level ◽  
Contact Surface ◽  
Vibration Amplitude ◽  
Sound Pressure ◽  
Pressure Level ◽  
Vibration Velocity ◽  
The Relationship ◽  
Velocity Level

Putting an ear close to a vibrating structure like a wall or a floor, we are able to hear structure-borne sounds clearly, but the loudness of such sounds has never been studied quantitatively. In this study, subjective experiments were carried out in order to obtain the relationship between loudness and the vibration amplitude of the ear's contact surface at low audible frequencies. The main result of this study is that the loudness of a structure-borne sound is almost equal to that of an air-borne sound with a sound pressure level 20 dB higher than the vibration velocity level (ref=5×10−8 m/s) of the surface. According to this result, the loudness of the structure-borne sound heard directly can be evaluated as a sound pressure level derived from the measured vibration amplitude of the structure.

The Relationship Between Nasal Sound Pressure Level and Palatopharyngeal Closure

1969 ◽  
Vol 12 (1) ◽  
pp. 193-198 ◽  
Author(s):  
Ralph L. Shelton ◽  
William B. Arndt ◽  
Albert W. Knox ◽  
Mary Elbert ◽  
Linda Chisum ◽  
...  
Keyword(s):  
Sound Pressure Level ◽  
Sound Pressure ◽  
Correlation Coefficients ◽  
Pressure Level ◽  
The Difference ◽  
The Relationship

A group of 21 subjects with well-fitted speech bulbs was compared for nasal sound pressure level (SPL) with a group of 13 subjects having moderate deficiency of palatopharyngeal closure. The difference in mean measures for the two groups was statistically significant. Correlation coefficients are reported for the relationships between nasal SPL and both a cinefluorographic measure of palatopharyngeal closure and several articulation measures.

Two Methods to Test Transducer Array Directivity

2014 ◽  
Vol 912-914 ◽  
pp. 1485-1488
Author(s):  
Hong Liu ◽  
Guo Zhu Zhao
Keyword(s):  
Sound Pressure Level ◽  
Sound Pressure ◽  
Beam Width ◽  
Directivity Pattern ◽  
Acute Angle ◽  
Pressure Level ◽  
The Other ◽  
Transducer Array ◽  
Acoustic Transducer ◽  
The One

An array which possess more array element number and whose frequency of the drive signal can be as large as possible in a range, directivity will be more preferable. On the other hand, when the structure of the sound radiating surface of the transducer or array layout is symmetrical, the corresponding directivity pattern will be symmetrical. In order to test transducer directivity, two methods are designed. The one is to measure the ultrasonic sound pressure level by instruments. The sound pressure level is measured at multiple points to deduce the directivity angle of the acoustic transducer array. The beam width of the 3×3 array is about at 23kHz, and the directivity acute angle is about 10°; higher frequencies will lead to the side lobes, but it can be negligible when compared to the main lobe. The other method is using the frequency analyzer to test transducer directivity in a silencer chamber. The sound pressure level can be read out from frequency response diagrams. The angle between the sound pressure value that decreasing 3db from the max value 111.7db and the max value is about 11°. So the directivity acute angle is about 11°. It should be noticed that, as the directivity diagram can not be directly attributed, there is some deviation in the conclusion.

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