The Effects of the Jet-Flow on Sound Propagation in Low-Speed Wind Tunnel

2012 ◽  
Vol 226-228 ◽  
pp. 368-373
Author(s):  
Yi Gang Wang ◽  
Jia Shun Yang ◽  
Yang Yang ◽  
Zhi Gang Yang
Keyword(s):  
Wind Tunnel ◽  
Sound Pressure Level ◽  
Sound Pressure ◽  
Sound Propagation ◽  
Prediction Method ◽  
Test Sample ◽  
Jet Flow ◽  
Pressure Level ◽  
High Frequency Signal ◽  
Low Speed Wind Tunnel

Based on the open-jet aero-acoustic wind tunnel, an experimental study was made to research the effects of the jet-flow on sound propagation. This study is focused on the changes of the direction of the sound propagation, the changes of the sound pressure level, the phenomenon of tone broadening and the availability of the existing prediction method for sound propagation in jet-flow. The results indicate that the influence of the jet-flow on the value of the noise source shift varies along the direction of the jet-flow and there is no regular influence on the sound pressure level. In addition, the flow around the test sample has affected the sound propagation, and the phenomenon of tone broadening exists when high frequency signal is used. The study also reveals the limitation of the application of the existing prediction method, because the model it used is too simple.

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.

Prediction and analysis of sound field in long enclosures with a modal-based method

2021 ◽  
Vol 69 (6) ◽  
pp. 518-529
Author(s):  
Changyong Jiang ◽  
Xiang Liu ◽  
Stephany Y. Xu ◽  
Shangyu Zhang
Keyword(s):  
Porous Material ◽  
Point Source ◽  
Sound Pressure Level ◽  
High Frequency ◽  
Sound Pressure ◽  
Prediction Method ◽  
Sound Field ◽  
Pressure Level ◽  
Noise Levels ◽  
Level Reduction

In this paper, the efficacy of porous ceiling treatment to reduce noise levels inside a typical tunnel is examined with a validated modal-based prediction method. It is found that, for a point source, the effect of increasing porous ceiling thickness on sound pressure level (SPL) attenuation along the tunnel is limited. A porous ceiling with thickness of 0.3 m is comparable with an infinite porous ceiling in middle and high frequency ranges. For a line source, the effect of ceiling thickness on SPL reduc- tion in this typical tunnel is limited. Sound pressure level reduction of 4 dBA is real- ized with 0.3 m porous ceiling, which is the same as infinite ceiling and only 1 dBA smaller than the theoretically optimized value. These results suggest that, in the event only ceiling treatment is considered, 0.3 m porous material is sufficient for noise re- duction in this typical tunnel.

A Study of Noise Generation on the E387, S823, NACA 0012, and NACA 4412 Airfoils for Use on Small-Scale Wind Turbines in the Urban Environment

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Kenneth W. Van Treuren ◽  
Andrew W. Hays
Keyword(s):  
Wind Tunnel ◽  
Wind Turbines ◽  
Sound Pressure Level ◽  
Sound Pressure ◽  
Reynolds Numbers ◽  
Pressure Level ◽  
Small Scale ◽  
Noise Prediction ◽  
Noise Generation ◽  
Naca 0012

Four airfoils typical to small-scale wind turbines were studied for noise generation: Eppler 387, NREL S823, NACA 0012, and NACA 4412. Wind tunnel sound pressure level (SPL) data were collected directly downstream of the airfoil for angles of attack from −10 deg to 25 deg and for Reynolds numbers from 50,000 to 200,000. Vertical and horizontal wake traverses define the extent of the noise generated. The data were analyzed by frequency and compared with a noise prediction from NREL AirFoil Noise (NAFNoise). The noise trends found can be applied to improve other airfoil selection when designing small-scale wind turbines.

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.

Acoustically Testing Stock and Modified UAS Propellers in Both the Near and Far Field

2020 ◽  
Author(s):  
Kenneth Van Treuren ◽  
Ricardo Sanchez ◽  
Charles Wisniewski ◽  
Paul Leitch
Keyword(s):  
Wind Tunnel ◽  
Sound Pressure Level ◽  
Sound Pressure ◽  
Sound Level ◽  
Pressure Level ◽  
Decay Rates ◽  
Urban Setting ◽  
Far Field ◽  
Field Noise ◽  
Noise Signature

Abstract In an urban setting, the sound level of a drone must be acceptable. This paper compares a stock DJI Phantom 2 propeller to a stock propeller modified with a Trailing Edge (TE) notch. The purpose was to determine the extent of the near and far field noise signature of the propellers. Measurements were taken in an anechoic chamber at measurement distances of 1 ft to 24 ft. Upstream of propeller, the sound decay follows the standard decay rate (6 dB decrease for a doubling of the distance) from a location of approximately 4 ft. Downstream the sound decay does not follow standard decay rates until 22 ft. A comparison of the two propellers shows that the TE notch and stock propellers have similar Sound Pressure Level (SPL) values at all distances measured. Traverse measurements downstream of the two propellers in the wind tunnel confirms that the magnitudes of the SPL values are similar after a distance of one foot, however, there does seem to be an influence of the TE notch on the frequency spectrum, shifting frequencies slightly higher. In addition to the single propeller tests, a DJI F550 Flame Wheel hexacopter was used to compare the stock and TE notch propellers. While the hexacopter was overall 20 dBA nosier, no discernable difference in SPL between the two propellers was measured.

Experimental Study on Screech Suppression of Supersonic Free Jet Through Rectangular Nozzle

2015 ◽  
Author(s):  
Zhe Chen ◽  
Jiu-Hui Wu ◽  
Xin Chen ◽  
Hao Lei ◽  
Adan Ren
Keyword(s):  
Experimental Study ◽  
Fundamental Frequency ◽  
Sound Pressure Level ◽  
High Frequency ◽  
Sound Pressure ◽  
Jet Flow ◽  
Pressure Level ◽  
Shock Cell ◽  
Free Jet ◽  
Rectangular Nozzle

The paper conducted a series of experimental study on V-shaped grooves influence of supersonic free jet through rectangular nozzles, such as two different screech modes, changing rules of sound pressure level of the screech mode, 3D-dynamic spectrum of sound pressure and schlieren photographs of the flow field. The experimental results show that V-shaped grooves on rectangular nozzle could reduce the acoustic feedback of shock wave from jet flow, so as to eliminate one mode of screech completely). It is also suggest that V-shaped grooves performed differently on rectangular nozzle compared with circular one at high frequency when jet pressure was high. Several fundamental frequency differentials exist in both two rectangular nozzles at the same pressure, whereas fundamental frequency in non V-grooved nozzle is much smoother than the V-grooved one. The nozzle with V-shaped grooves had a significant noise suppression effect below 0.55MPa. An instantaneous spectrum comparison between V-grooved and non V-grooved nozzles in scope of 0.25∼0.40MPa was given. The SPL (Sound Pressure Level) differential increased at beginning, then decreased with the decline of jet pressure in low frequency below 10kHz. Nozzle with V-shaped grooves had a lower SPL. Nevertheless, an entirely different phenomenon was discovered in high frequency above 10kHz. When jet pressure was 0.40MPa, V-grooved rectangular nozzle had a higher SPL, and it approached to SPL of non V-grooved nozzle with decline of jet pressure until below it. Moreover, differentials gradually became obvious due to the mixing effect with different nozzle structure. Noise pressure in V-grooved nozzle dropped rapidly in range of 0.40∼0.80MPa, as well as lower SPL and widely frequency distribution. Impact of V-shaped grooves on schlieren photographs was analyzed. Flow at nozzle exit was strengthened by impact of V-shaped grooves. An obviously density gradient could be found in first shock-cell and length of cell was smaller than the one without grooves. The flow was more stable in other cells but in a weaker intensity. The V-shaped grooves could increase length of jet path as well as decrease expansion of the cells. In general, V-shaped grooves in rectangular nozzle performed differently from circular nozzle, which could suppress and even eliminate jet flow screech. During engineering application, the matching of V-shaped grooves in rectangular nozzle and pressure of jet flow should be taken into consider.

Contributions of Voice and Nonverbal Communication to Perceived Masculinity–Femininity for Cisgender and Transgender Communicators

2020 ◽  
Vol 63 (4) ◽  
pp. 931-947
Author(s):  
Teresa L. D. Hardy ◽  
Carol A. Boliek ◽  
Daniel Aalto ◽  
Justin Lewicke ◽  
Kristopher Wells ◽  
...  
Keyword(s):  
Fundamental Frequency ◽  
Sound Pressure Level ◽  
Sound Pressure ◽  
Vocal Tract ◽  
Presentation Mode ◽  
Pressure Level ◽  
Presentation Modes ◽  
Audiovisual Stimuli ◽  
Vocal Tract Resonance ◽  
Point Light

Purpose The purpose of this study was twofold: (a) to identify a set of communication-based predictors (including both acoustic and gestural variables) of masculinity–femininity ratings and (b) to explore differences in ratings between audio and audiovisual presentation modes for transgender and cisgender communicators. Method The voices and gestures of a group of cisgender men and women ( n = 10 of each) and transgender women ( n = 20) communicators were recorded while they recounted the story of a cartoon using acoustic and motion capture recording systems. A total of 17 acoustic and gestural variables were measured from these recordings. A group of observers ( n = 20) rated each communicator's masculinity–femininity based on 30- to 45-s samples of the cartoon description presented in three modes: audio, visual, and audio visual. Visual and audiovisual stimuli contained point light displays standardized for size. Ratings were made using a direct magnitude estimation scale without modulus. Communication-based predictors of masculinity–femininity ratings were identified using multiple regression, and analysis of variance was used to determine the effect of presentation mode on perceptual ratings. Results Fundamental frequency, average vowel formant, and sound pressure level were identified as significant predictors of masculinity–femininity ratings for these communicators. Communicators were rated significantly more feminine in the audio than the audiovisual mode and unreliably in the visual-only mode. Conclusions Both study purposes were met. Results support continued emphasis on fundamental frequency and vocal tract resonance in voice and communication modification training with transgender individuals and provide evidence for the potential benefit of modifying sound pressure level, especially when a masculine presentation is desired.

Case study: Theoretical calculation model and variable condition analysis research on the water-splashing noise for natural draft wet cooling towers

2020 ◽  
Vol 68 (2) ◽  
pp. 137-145
Author(s):  
Yang Zhouo ◽  
Ming Gao ◽  
Suoying He ◽  
Yuetao Shi ◽  
Fengzhong Sun
Keyword(s):  
Theoretical Model ◽  
Sound Pressure Level ◽  
Water Droplet ◽  
Water Distribution ◽  
Sound Pressure ◽  
Cooling Tower ◽  
Distribution Patterns ◽  
Calculation Model ◽  
Pressure Level ◽  
Cooling Towers

Based on the basic theory of water droplets impact noise, the generation mechanism and calculation model of the water-splashing noise for natural draft wet cooling towers were established in this study, and then by means of the custom software, the water-splashing noise was studied under different water droplet diameters and water-spraying densities as well as partition water distribution patterns conditions. Comparedwith the water-splashing noise of the field test, the average difference of the theoretical and the measured value is 0.82 dB, which validates the accuracy of the established theoretical model. The results based on theoretical model showed that, when the water droplet diameters are smaller in cooling tower, the attenuation of total sound pressure level of the water-splashing noise is greater. From 0 m to 8 m away from the cooling tower, the sound pressure level of the watersplashing noise of 3 mm and 6 mm water droplets decreases by 8.20 dB and 4.36 dB, respectively. Additionally, when the water-spraying density becomes twice of the designed value, the sound pressure level of water-splashing noise all increases by 3.01 dB for the cooling towers of 300 MW, 600 MW and 1000 MW units. Finally, under the partition water distribution patterns, the change of the sound pressure level is small. For the R s/2 and Rs/3 partition radius (Rs is the radius of water-spraying area), when the water-spraying density ratio between the outer and inner zone increases from 1 to 3, the sound pressure level of water-splashing noise increases by 0.7 dB and 0.3 dB, respectively.

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