The formula for sound pressure level outside a building containing a noise source

A hybrid-type noise control method is applied to fundamental and higher-order blade-passing frequency components, abbreviated to BPF components, radiated from a centrifugal blower. An active cancellation of the BPF noise source is conducted based on a detailed investigation of the noise source distribution by using correlation analysis. The sound pressure level of 2nd- and/or 3rd-order BPF can be reduced by more than 15 decibels and discrete tones almost eliminate from the power spectra of blower-radiated noise. On the other hand, the sound pressure level of the fundamental BPF is difficult to reduce effectively by the active cancellation method because of the large amplitude of the noise source fluctuation. However, the fundamental BPF is largely influenced by the frequency-response characteristics of the noise transmission passage, and is passively reduced by appropriate adjusting of the inlet duct length. Simultaneous reduction of BPF noise, therefore, can be easily made possible by applying passive and active control methods on the fundamental and higher-order BPF noise, respectively. We also discuss the distribution pattern of BPF noise sources by numerical simulation of flow fields around the scroll cutoff.

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Numerical and Experimental Investigation on Radiated Noise Characteristics of the Multistage Centrifugal Pump

Processes ◽

10.3390/pr7110793 ◽

2019 ◽

Vol 7 (11) ◽

pp. 793 ◽

Cited By ~ 5

Author(s):

Si ◽

Wang ◽

Yuan ◽

Huang ◽

Lin ◽

...

Keyword(s):

Centrifugal Pump ◽

Sound Pressure Level ◽

Sound Pressure ◽

Noise Source ◽

Low Noise ◽

Pressure Level ◽

Radiated Noise ◽

Noise Characteristics ◽

Flow Induced Noise ◽

Multistage Pump

The radiated noise of the centrifugal pump acts as a disturbance in many applications. The radiated noise is closely related to the hydraulic design. The hydraulic parameters in the multistage pump are complex and the flow interaction among different stages is very strong, which in turn causes vibration and noise problems because of the strong hydraulic excitation. Hence, the mechanism of radiated noise and its relationship with hydraulics must be studied clearly. In order to find the regular pattern of the radiated noise at different operational conditions, a hybrid numerical method was proposed to obtain the flow-induced noise source based on Lighthill acoustic analogy theory, which divided the computational process into two parts: computational fluid dynamics (CFD) and computational acoustics (CA). The unsteady flow field was solved by detached eddy simulation using the commercial CFD code. The detailed flow information near the surface of the vane diffusers and the calculated flow-induced noise source was extracted as the hydraulic exciting force, both of which were used as acoustic sources for radiated noise simulation. The acoustic simulation employed the finite element method code to get the sound pressure level (SPL), frequency response, directivity, et al. results. The experiment was performed inside a semi-anechoic room with a closed type pump test rig. The pump performance and acoustic parameters of the multistage pump at different flow rates were gathered to verify the numerical methods. The computational and experimental results both reveal that the radiated noise exhibits a typical dipole characteristic behavior and its directivity varies with the flowrate. In addition, the sound pressure level (SPL) of the radiated noise fluctuates with the increment of the flow rate and the lowest SPL is generated at 0.8Qd, which corresponds to the maximum efficiency working conditions. Furthermore, the experiment detects that the sound pressure level of the radiated noise in the multistage pump rises linearly with the increase of the rotational speed. Finally, an example of a low noise pump design is processed based on the obtained noise characteristics.

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Noise Source Identification and Noise Directivity Analysis of Bladeless Fans by Combined CFD and CAA Method

Volume 1: Fluid Applications and Systems; Fluid Measurement and Instrumentation ◽

10.1115/fedsm2020-20168 ◽

2020 ◽

Author(s):

Ang Li ◽

Jun Chen ◽

Yangfan Liu ◽

J. Stuart Bolton ◽

Patricia Davies

Keyword(s):

Sound Pressure Level ◽

Sound Pressure ◽

Noise Source ◽

Near Field ◽

Low Noise ◽

Pressure Level ◽

Design Stage ◽

Source Analysis ◽

Far Field ◽

Computational Domain

Abstract The bladeless fan is a new concept of fan that does not have visible impellers. It features low noise level, uniform airflow, and improved safety. It has been widely applied in household appliances. Since the customers are particularly sensitive to the noise generated by the fan, the aeroacoustics performance of the fan needs to be accurately characterized in the design stage. In this study, computational fluid dynamic (CFD) and computational aeroacoustics (CAA) are applied to investigate the aeroacoustics performance and identify the major noise source of the bladeless fan. A prototype of the bladeless fan, including a wind channel, a base cavity, a rotor and a stator inside the base, is set in a computational domain of 4m × 2m × 2m and the airflow through the fan is simulated. The hybrid mesh is generated, the unstructured mesh in the near field, and the structured at the far field. To compute the flow field, steady RANS simulation (standard k–ε turbulence model) and Large Eddy simulation (Smagorinsky-Lilly model) are carried out. Ffowcs Williams and Hawkings (FW-H) analogy is used to predict the acoustic field. Experiments, including air velocity measurement and sound pressure measurement, are conducted to validate simulation results. Sound pressure level results at the near-field receiver illustrate that the blade passage frequency can be captured by combined CFD and CAA method. Noise source analysis shows that the combination of the rotor and stator contributes most to the noise produced by the bladeless fan. The wind channel is the secondary source. Sound pressure level contours at different distances and different heights are generated to investigate the directivity pattern of the noise generated by the bladeless fan. At the near field, the produced noise at the front and the back of the bladeless fan are louder than those at left and right; at the far field, the noise at the front is much larger than the other three sides. In addition, at the near field, with the increase of the height, two separated hotspots appear over 2,500Hz and the sound pressure level at these two hotspots increases; at the far field, the noise distribution at different heights is similar and the peak near 3,000Hz can be estimated. A possible reason to cause this peak is vortex shedding at the trailing edge of the rotor’s blades. The aeroacoustics analysis is helpful to develop strategies to reduce noise and guide the improved design of the bladeless fan.

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

Journal of Speech Language and Hearing Research ◽

10.1044/2019_jslhr-19-00387 ◽

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.

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Computers and Electronics in Agriculture The sensor to estimate the sound pressure level in eggs

Qeios ◽

10.32388/7x11uf ◽

2020 ◽

Author(s):

Iran Oliveira Silva

Keyword(s):

Sound Pressure Level ◽

Sound Pressure ◽

Pressure Level

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

Noise Control Engineering Journal ◽

10.3397/1/376812 ◽

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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