Acoustic characteristics of wall jets over a rough surface

2020 ◽  
Vol 68 (5) ◽  
pp. 316-327
Author(s):  
Rahul S. Arackal ◽  
T.J.S. Jothi
Keyword(s):  
Surface Roughness ◽  
Rough Surface ◽  
Smooth Surface ◽  
Sound Pressure ◽  
Acoustic Measurements ◽  
Frequency Range ◽  
Noise Levels ◽  
Wall Jets ◽  
Acoustic Characteristics ◽  
Plate Length

The effects of surface roughness on the noise emissions from wall jets with a plate length (L) of 40 cm are presented in this article. The surface roughness of the plate considered for the study is in the range of 5 to 19 mm, and the jet velocity at the nozzle exit is varied from 20 to 56 m/s. Acoustic measurements of the different roughness plate wall jets are carried out at a distance of 60 cm from the jet axis and compared with that of a smooth surface. The spectral results indicate that the noise emissions from rough surface wall jets are lower in the frequency range (0.3â–“3.0 kHz), and the corresponding sound pressure levels are lower by around 5 dB compared to the noise from a smooth surface. Concurrently, the surface roughness is significant in generating higher noise levels by around 5 dB in the frequency range of 3 to 12 kHz compared to its counterpart.

scholarly journals Measurement and Analysis of Infrasound Signals Generated by Operation of High-Power Wind Turbines

Energies ◽  
2021 ◽  
Vol 14 (20) ◽  
pp. 6544
Author(s):  
Tomasz Malec ◽  
Tomasz Boczar ◽  
Daria Wotzka ◽  
Michał Kozioł
Keyword(s):  
Wind Turbines ◽  
High Power ◽  
Sound Pressure ◽  
Operating Time ◽  
Weather Conditions ◽  
Acoustic Energy ◽  
Working Environment ◽  
Frequency Range ◽  
Noise Levels ◽  
Measurement And Analysis

The development of wind energy and the increasing number of installed wind turbines make it necessary to assess them in terms of the nuisance of the emitted infrasound noise generated by such devices. The article presents the results of measurements and analyses of infrasound emitted during the operation of wind turbines installed in various locations in Poland. Comparative analysis of noise levels in the infrasound and audible range has shown that acoustic energy is mainly in the low and infrasound frequency range, and the measured levels depend significantly on the weighting curves used. On the basis of the results, it was confirmed that the sound pressure level of infrasound signals emitted by the operation of high-power wind turbines, regardless of wind velocity, weather conditions, design solutions of turbines, operating time, rated capacity, does not exceed the criteria specified in the applicable legislation dealing with the assessment of infrasound noise on the working environment.

scholarly journals Review of Acoustic Sources Alternatives to a Dodecahedron Speaker

2019 ◽  
Vol 9 (18) ◽  
pp. 3705 ◽  
Author(s):  
Nikolaos M. Papadakis ◽  
Georgios E. Stavroulakis
Keyword(s):  
High Frequency ◽  
Sound Pressure ◽  
Transfer Functions ◽  
Acoustic Measurements ◽  
Acoustic Source ◽  
Acoustic Characteristics ◽  
Acoustic Sources ◽  
Future Work ◽  
Selection Of ◽  
Better Than

An omnidirectional source is required in many acoustic measurements. Commonly a dodecahedron speaker is used but due to various factors (e.g., high cost, transportation difficulties) other acoustic sources are sometimes preferred. In this review, fifteen acoustic source alternatives to a dodecahedron speaker are presented while emphasis is placed on features such as omnidirectionality, repeatability, adequate sound pressure levels, even frequency response, accuracy in measurement of acoustic parameters and fulfillment of ISO 3382-1 source requirements. Some of the alternative acoustic sources have the appropriate features to provide usable results for acoustic measurements, some have acoustic characteristics better than a dodecahedron speaker (e.g., omnidirectionality in the high-frequency range), while some can potentially fulfill the ISO 3382-1 source requirements. Collected data from this review can be used in many areas (e.g., ISO measurements, head-related transfer functions measurements) for the appropriate selection of an acoustic source according to the expected use. Finally, suggestions for uses and future work are given aimed at achieving further advances in this field.

scholarly journals Estimation of losses per unit length in a rectangular waveguide with rough screening surfaces based on the concept of partial waves

2019 ◽  
Vol 30 ◽  
pp. 07001
Author(s):  
Vladimir Biryukov ◽  
Vladimir Grachev ◽  
Ekaterina Karakozova ◽  
Sergey Lobin ◽  
Vladimir Shcherbakov
Keyword(s):  
Surface Roughness ◽  
Electromagnetic Wave ◽  
Rough Surface ◽  
Rectangular Waveguide ◽  
Unit Length ◽  
Surface Profile ◽  
Terahertz Frequency ◽  
Frequency Range ◽  
Terahertz Frequency Range ◽  
Surface Reflection

A method for calculating the rough surface reflection coefficient of an electromagnetic wave is proposed. It is shown that the screening surface roughness in waveguides is equivalent to a decrease in conductivity of these surfaces in comparison with values belonging to Schukin-Leontovich boundary conditions for completely smooth surfaces. Examples of calculating the attenuation coefficient in the rectangular waveguide with rough screening surfaces in a terahertz frequency range are presented. The influence of the size and shape of the rough surface profile irregularities on the waveguide attenuation is studied.

Role of Plate Length on Noise from Wall Jets

2019 ◽  
Vol 105 (6) ◽  
pp. 928-942
Author(s):  
Rahul S. Arackal ◽  
T. J. S. Jothi
Keyword(s):  
Shear Layer ◽  
Strouhal Number ◽  
Frequency Noise ◽  
Noise Levels ◽  
Noise Emission ◽  
Wall Jets ◽  
Trailing Edge ◽  
Number Range ◽  
Nozzle Height ◽  
Plate Length

The present study experimentally investigates the effect of the growth of inner layer on noise emission characteristics of wall jets. The plate length L considered for the current study vary in the range of L/h = 2.5 to 30, where h is the nozzle height. The jet is issued from a nozzle having the exit dimensions of 20 cm in width and 2 cm in height h. The jet Reynolds number, based on the nozzle height and jet exit velocity Uj, is varied up to 7.0 · 104. Acoustic measurements revealed the distinct variations in the noise levels with different plate lengths. The L/h = 2.5 wall jet has an increase in noise levels by around 10 dB compared to that of a free jet (background noise). Wall jets in the range of L/h = 5 to 20 radiate higher noise levels compared to other plates, while the least noise emissions are observed from fully developed wall jets (L/h > 20). The significant sources identified for noise emissions are the trailing edge and the secondary shear layer in the wall jets. The low frequency noise corresponding to the Strouhal number (based on h) below 0.2 is characterized as the trailing edge noise. The spectra of the wall jets collapse in the Strouhal number range (based on the inner layer thickness of wall jets) of ∼0.2 to 1.0 indicating the secondary shear layer noise of wall jets.

Effect of Surface Roughness on Fouling of Calcium Carbonate: An Experimental Investigation

2010 ◽  
Author(s):  
M. Izadi ◽  
D. K. Aidun ◽  
P. Marzocca ◽  
H. Lee
Keyword(s):  
Surface Roughness ◽  
Calcium Carbonate ◽  
Rough Surface ◽  
Smooth Surface ◽  
Rough Surfaces ◽  
Operating Conditions ◽  
Tubular Heat Exchanger ◽  
Analytical Microscopy ◽  
Deposit Layer ◽  
Effect Of Surface

The effect of surface roughness on the fouling behavior of calcium carbonate is experimentally investigated. The real operating conditions of a tubular heat exchanger are simulated by performing prolonged experiments with duration of 3 to 7 days. The solution used is a mixture of sodium bicarbonate and calcium chloride in de-ionized water with the concentration of 0.4 g/l of each. An on-line fouling evaluation system was developed such that the fouling resistance for a selected solution could be measured in real time. The experiments are repeated with the same procedure for 90/10 Cu/Ni tubes with different internal surface roughness. After the experiment the surface is analyzed by analytical microscopy to investigate the morphology of the deposit layer. Comparison of the experimental results of smooth and rough surfaces shows that a combination of aragonite and calcite polymorphs are formed on rough surface while only dendritic porous aragonite crystals are formed on smooth surface. Accordingly, the deposit layer formed on rough surface is denser and has a higher thermal resistance comparing to that formed on smooth surface. The fouling factor-time curves of smooth and rough surfaces obtained by the current experimental study agree with the results found by the analytical microscopy of the surface and show higher fouling resistances for rough surface. Experimental data is significantly important for the design, and formulating operating, and cleaning schedules of the equipment.

Effect of soil surface roughness and scene components on soil surface bidirectional reflectance factor

2012 ◽  
Vol 92 (2) ◽  
pp. 297-313 ◽  
Author(s):  
Z. Wang ◽  
C. A. Coburn ◽  
X. Ren ◽  
P. M. Teillet
Keyword(s):  
Surface Roughness ◽  
Rough Surface ◽  
Zenith Angle ◽  
Smooth Surface ◽  
Soil Surface ◽  
Bidirectional Reflectance ◽  
Imaging Spectrometer ◽  
Bidirectional Reflectance Factor ◽  
Reflectance Factor ◽  
Soil Surface Roughness

Wang, Z., Coburn, C. A., Ren, X. and Teillet, P. M. 2012. Effect of soil surface roughness and scene components on soil surface BRF. Can. J. Soil Sci. 92: 297–313. Bidirectional Reflectance factor (BRF) data of both rough [surface roughness index (SRI) of 51%] and smooth soil surfaces (SRI of 5%) were acquired in the laboratory under 30° illumination zenith angle using a Specim V10E imaging spectrometer and an Ocean Optics non-imaging spectrometer mounted on the University of Lethbridge Goniometer System version 2.5 (ULGS-2.5) and version 2.0 (ULGS-2.0), respectively. Under controlled laboratory conditions, the rough soil surface exhibited higher spectral reflectance than the smooth surface for most viewing angles. The BRF of the rough surface varied more than the smooth surface as a function of the viewing zenith angle. The shadowing effect was stronger for the rough surface than for the smooth surface and was stronger in the forward-scattering direction than in the backscattering direction. The pattern of the BRF generated with the non-image based data was similar to that generated with the whole region of interest (ROI) of the image-based data, and that of the whole ROI of the image-based data was similar to that of the illuminated scene component. The BRF of the smooth soil surface was dominated by illuminated scene component, i.e., the sunlit pixels, whereas the shaded scene component, i.e., the shaded pixels, was a larger proportion of the BRF of the rough soil surface. The image-based approach allowed the characterization of the contribution of spatial components in the field of view to soil BRF and improved our understanding of soil reflectance.

scholarly journals Prediction of Turbulent Boundary Layer Induced Noise in the Cabin of a BWB Aircraft

2012 ◽  
Vol 19 (4) ◽  
pp. 693-705 ◽  
Author(s):  
Joana Rocha ◽  
Afzal Suleman ◽  
Fernando Lau
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Sound Pressure ◽  
Pressure Level ◽  
Interior Noise ◽  
Analytical Models ◽  
Frequency Range ◽  
Noise Levels ◽  
Cabin Noise ◽  
Cabin Interior

This paper discusses the development of analytical models for the prediction of aircraft cabin noise induced by the external turbulent boundary layer (TBL). While, in previous works, the contribution of an individual panel to the cabin interior noise was considered, here, the simultaneous contribution of multiple flow-excited panels is analyzed. Analytical predictions are presented for the interior sound pressure level (SPL) at different locations inside the cabin of a Blended Wing Body (BWB) aircraft, for the frequency range 0–1000 Hz. The results show that the number of vibrating panels significantly affects the interior noise levels. It is shown that the average SPL, over the cabin volume, increases with the number of vibrating panels. Additionally, the model is able to predict local SPL values, at specific locations in the cabin, which are also affected with by number of vibrating panels, and are different from the average values.

scholarly journals On the influence of lateral cells and local perforation of resonance liner samples on the accuracy of determining their acoustic characteristics in experimental studies

2020 ◽  
Vol 320 ◽  
pp. 00018
Author(s):  
Oleg Kustov ◽  
Igor Khramtsov
Keyword(s):  
Sound Pressure ◽  
Experimental Studies ◽  
Normal Wave ◽  
Single Layer ◽  
Frequency Range ◽  
Acoustic Characteristics ◽  
Layer Sample ◽  
Honeycomb Cell ◽  
Research Recommendations ◽  
Wave Incidence

When determining the acoustic characteristics of a single-layer sample of a honeycomb liner by experiments in interferometers with normal wave incidence, a significant effect of incomplete lateral cells of the sample on acoustic characteristics was revealed. The experiments were carried out on two interferometers with channel diameters of 30 and 50 mm in the frequency range 500-3500 Hz at sound pressure levels of 120-155 dB. Based on the results of the experiments, an assessment was made of the effect on the acoustic characteristics of the percentage of perforation, which is the same both for one honeycomb cell and for the entire SAS sample. Based on the results of the research, recommendations were made to improve the accuracy of obtaining the acoustic characteristics of samples of honeycomb liner when testing them in interferometers of normal wave incidence.

scholarly journals Acoustic Characteristics of the Cabin of the Research Platform on the Airbag IL-PRC-600m

2018 ◽  
Vol 2018 (2) ◽  
pp. 16-23 ◽  
Author(s):  
Sławomir Cieślak ◽  
Wiesław Krzymień ◽  
Krzysztof Szafran
Keyword(s):  
Sound Pressure ◽  
Noise Exposure ◽  
Occupational Noise ◽  
Test Results ◽  
Acoustic Measurements ◽  
Acoustic Characteristics ◽  
Water Ice ◽  
Flat Surfaces ◽  
Occupational Noise Exposure ◽  
Research Platform

Abstract Hovercrafts are a universal means of transport intended for use on flat surfaces such as water, ice, snow, swamp, or sand. They are used in rescue operations and patrolling difficult areas inaccessible to other means of transport. The Institute of Aviation conducted acoustic measurements inside the cabin of the hovercraft to determine the source of the noise and the sound pressure exerted on the pilot and passengers. Assessment of the sources of noise in the cabin is made using the acoustic beamforming method. Assessment of the level of noise to which a pilot is exposed during the operation was prepared on the basis of a standard specifying the requirements and methods of determining occupational noise exposure [1]. The test results indicate a significant penetration of noise from the drivetrain into the cabin. It is recommended that a hovercraft pilot and operators use hearing protection in some specified conditions and during testing. Thus it is pointed out in the summary that additional soundproofing of the cabin is needed. The points of the greatest penetration of noise into the interior have been indicated.

The acoustic advantage of hunting at low heights above water: behavioural experiments on the European ‘trawling’ bats Myotis capaccinii, M. dasycneme and M. daubentonii

2001 ◽  
Vol 204 (22) ◽  
pp. 3843-3854
Author(s):  
Björn M. Siemers ◽  
Peter Stilz ◽  
Hans-Ulrich Schnitzler
Keyword(s):  
Smooth Surface ◽  
Sound Pressure ◽  
Foraging Strategy ◽  
Pressure Level ◽  
Acoustic Properties ◽  
Acoustic Characteristics ◽  
The World ◽  
Calm Water ◽  
Behavioural Experiments ◽  
Different Parts

SUMMARY We have demonstrated in behavioural experiments that success in capturing prey from surfaces in ‘trawling Myotis’ (Leuconoë-type) depends on the acoustic properties of the surface on which the prey is presented. Two types of surface structure were ensonified with artificial bat signals to probe their acoustic characteristics. We have shown that perception of prey by echolocation is easier if the prey is presented on a smooth surface (such as calm water) than if it is presented on a structured surface (such as vegetation or the ground). This is because the smooth surface reflects a much lower level of clutter echoes than the structured one if ensonified at an angle typical for bats foraging low over water. The ensonification experiments revealed that the sound pressure level of the echo was even higher for mealworms on a smooth surface than for mealworms suspended in air. This might be because waves travelling via the surface also contribute to the echo (e.g. reflection from the surface to the mealworm, back to the surface and then to the receiver). From the behavioural experiments, we conclude that ‘trawling Myotis’ take isolated objects on smooth (water) surfaces for prey. Those objects reflect isolated, stationary acoustic glints back to the echolocating bats. Conversely, ‘trawling Myotis’ will not recognise prey if prey echoes are embedded in numerous clutter echoes. We have demonstrated marked similarities between the three European ‘trawling Myotis’ species M. dasycneme, M. daubentonii and M. capaccinii in echolocation behaviour, search image, foraging strategy and prey perception. We propose that a combination of prey abundance and acoustic advantages could have led to repeated and convergent evolution of ‘trawling’ bats in different parts of the world.

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