On high-frequency noise scattering by aerofoils in flow

2013 ◽  
Vol 734 ◽  
pp. 144-182 ◽  
Author(s):  
Lorna J. Ayton ◽  
N. Peake
Keyword(s):  
Transition Region ◽  
High Frequency ◽  
Angle Of Attack ◽  
Outer Region ◽  
Frequency Noise ◽  
Sound Waves ◽  
Incident Wavelength ◽  
Singular Perturbation Analysis ◽  
Trailing Edges ◽  
Valid Solution

AbstractA theoretical model is developed for the sound scattered when a sound wave is incident on a cambered aerofoil at non-zero angle of attack. The model is based on the linearization of the Euler equations about a steady subsonic flow, and is an adaptation of previous work which considered incident vortical disturbances. Only high-frequency sound waves are considered. The aerofoil thickness, camber and angle of attack are restricted such that the steady flow past the aerofoil is a small perturbation to a uniform flow. The singular perturbation analysis identifies asymptotic regions around the aerofoil; local ‘inner’ regions, which scale on the incident wavelength, at the leading and trailing edges of the aerofoil; Fresnel regions emanating from the leading and trailing edges of the aerofoil due to the coalescence of singularities and points of stationary phase; a wake transition region downstream of the aerofoil leading and trailing edge; and an outer region far from the aerofoil and wake. An acoustic boundary layer on the aerofoil surface and within the transition region accounts for the effects of curvature. The final result is a uniformly-valid solution for the far-field sound; the effects of angle of attack, camber and thickness are investigated.

scholarly journals On high-frequency sound generated by gust–aerofoil interaction in shear flow

2015 ◽  
Vol 766 ◽  
pp. 297-325 ◽  
Author(s):  
Lorna J. Ayton ◽  
N. Peake
Keyword(s):  
Shear Flow ◽  
Transition Region ◽  
High Frequency ◽  
Outer Region ◽  
Far Field ◽  
Radiated Power ◽  
Surface Transition ◽  
Trailing Edges ◽  
Parallel Shear Flow ◽  
Field Sound

AbstractA theoretical model is constructed to predict the far-field sound generated by high-frequency gust–aerofoil interaction in steady parallel shear flow, including the effects of aerofoil thickness. Our approach is to use asymptotic analysis of the Euler equations linearised about steady parallel shear flow, in the limits of high frequency and small, but non-zero, aerofoil thickness and Mach number. The analysis splits the flow into various regions around the aerofoil; local inner regions around the leading and the trailing edges where sound is generated and scattered; a surface transition region accounting for the curvature of the aerofoil; a wake transition region downstream of the aerofoil; and an outer region through which the sound propagates to the observer. Solutions are constructed in all regions, and matched using the principle of matched asymptotic expansions to yield the first two terms in the expansion of both the amplitude and the phase of the far-field pressure. Result are computed for the particular case of scattering of a gust by a symmetric Joukowski aerofoil placed in symmetric Gaussian parallel shear flow. The introduction of mean shear is shown to have a significant effect on the far-field directivity and on the total radiated power.

scholarly journals HIGH FREQUENCY NOISE IN LAKE BAIKAL AS A BACKGROUND FOR THE ACOUSTIC DETECTION OF HIGH ENERGY NEUTRINOS

2006 ◽  
Vol 21 (supp01) ◽  
pp. 117-121 ◽  
Author(s):  
V. M. AYNUTDINOV ◽  
V. A. BALKANOV ◽  
I. A. BELOLAPTIKOV ◽  
L. B. BEZRUKOV ◽  
D. A. BORSCHEV ◽  
...  
Keyword(s):  
Lake Baikal ◽  
High Frequency ◽  
Acoustic Noise ◽  
High Energy ◽  
Frequency Noise ◽  
Acoustic Detection ◽  
Sound Waves ◽  
Neutrino Detection ◽  
Ongoing Work ◽  
High Energy Neutrinos

We review the ongoing work of the Baikal Collaboration on acoustic detection of super high energy neutrinos. Some results of the study of high frequency acoustic noise in Lake Baikal are presented. A lot of short impulses with different amplitudes and shapes were detected, which should be considered as a background for acoustic neutrino detection. However, most of the short impulses appear to be due to noise sound waves interference and can be eliminated by a correlation analysis. Only a few detected bipolar impulses probably were produced by quasi local sources.

Influence of incidence angle on sound generation by airfoils interacting with high-frequency gusts

1995 ◽  
Vol 292 ◽  
pp. 271-304 ◽  
Author(s):  
Matthew R. Myers ◽  
E. J. Kerschen
Keyword(s):  
High Frequency ◽  
Incidence Angle ◽  
Outer Region ◽  
Sound Field ◽  
Leading Edge ◽  
Edge Region ◽  
Sound Generation ◽  
Mean Flow ◽  
Flow Stagnation ◽  
Trailing Edges

A theoretical model is developed for the sound generated when a convected vortical or entropic gust encounters an airfoil at non-zero angle of attack. The theory is based on a linearization of the Euler equations about the steady subsonic flow past the airfoil. High-frequency gusts, whose wavelengths are short compared to the airfoil chord, but long compared to the displacement of the mean-flow stagnation point from the leading edge, are considered. The analysis utilizes singular-perturbation techniques and involves four asymptotic regions. Local regions, which scale on the gust wavelength, are present at the airfoil leading and trailing edges. Behind the airfoil a ‘transition’ region, which is similar to the transition zone between illuminated and shadow zones in optical problems, is present. In the outer region, far away from the airfoil edges and wake, the solution has a geometric-acoustics form. The primary sound generation is found to be concentrated in the local leading-edge region. The trailing edge plays a secondary role as a scatterer of the sound generated in the leading-edge region. Parametric calculations are presented which illustrate that moderate levels of airfoil steady loading can significantly affect the sound field produced by airfoil–gust interactions.

Effect of Aggregate Size and Gradation on the Ceramsite Sound-Absorbing Materials

2011 ◽  
Vol 216 ◽  
pp. 450-457
Author(s):  
Xiang Yu Luo ◽  
Wen Fang Li ◽  
Xue Li Jin
Keyword(s):  
Mechanical Properties ◽  
High Frequency ◽  
Sound Absorption ◽  
Pore Diameter ◽  
Aggregate Size ◽  
Effective Porosity ◽  
Diameter Distribution ◽  
Frequency Noise ◽  
Sound Waves ◽  
Absorbing Materials

In this paper, the effect of ceramsite aggregate size and gradation on the sound absorption and mechanical properties of the materials were studied and the relationship between material’s pore structure and its sound absorption were discussed. It can be found from the results that the sound absorption and mechanical properties of the ceramsite sound-absorbing materials increase with the content of the fine ceramsite increased due to the decrease of the median pore diameter of the ceramsite sound-absorbing materials where the improvement of the sound absorption at the high frequency band is more significant suggesting that fine pores have a better sound-absorbing effect for high-frequency noise. Higher effective porosity doesn’t mean better sound absorption, because materials with coarse pores have shorter internal routes for sound waves and less friction during sound waves passing through pores, which conversely decreases the material’s sound absorption. Ceramsite with higher internal porosity and more uniform pore diameter distribution can produce materials with better sound absorption.

Case study: Simulation and control of high frequency noise for commercial vehicle cab considering leak

2019 ◽  
Vol 67 (4) ◽  
pp. 315-329
Author(s):  
Rongjiang Tang ◽  
Zhe Tong ◽  
Weiguang Zheng ◽  
Shenfang Li ◽  
Li Huang
Keyword(s):  
High Frequency ◽  
Commercial Vehicle ◽  
Frequency Noise ◽  
High Frequency Noise ◽  
Simulation And Control ◽  
And Control

Aerodynamic noise from an asymmetric airfoil with perforated extension plates at the trailing edge

2020 ◽  
pp. 1475472X2097838
Author(s):  
CK Sumesh ◽  
TJS Jothi
Keyword(s):  
High Frequency ◽  
Sound Pressure ◽  
Pore Diameter ◽  
Low Frequency ◽  
Aerodynamic Noise ◽  
Frequency Noise ◽  
Low Frequency Noise ◽  
Trailing Edge ◽  
High Frequency Noise ◽  
Displacement Thickness

This paper investigates the noise emissions from NACA 6412 asymmetric airfoil with different perforated extension plates at the trailing edge. The length of the extension plate is 10 mm, and the pore diameters ( D) considered for the study are in the range of 0.689 to 1.665 mm. The experiments are carried out in the flow velocity ( U∞) range of 20 to 45 m/s, and geometric angles of attack ( αg) values of −10° to +10°. Perforated extensions have an overwhelming response in reducing the low frequency noise (<1.5 kHz), and a reduction of up to 6 dB is observed with an increase in the pore diameter. Contrastingly, the higher frequency noise (>4 kHz) is observed to increase with an increase in the pore diameter. The dominant reduction in the low frequency noise for perforated model airfoils is within the Strouhal number (based on the displacement thickness) of 0.11. The overall sound pressure levels of perforated model airfoils are observed to reduce by a maximum of 2 dB compared to the base airfoil. Finally, by varying the geometric angle of attack from −10° to +10°, the lower frequency noise is seen to increase, while the high frequency noise is observed to decrease.

scholarly journals Musik Gamelan Bali Meningkatkan Pertumbuhan dan Produktivitas Tanaman Sawi Pakcoy (Brassica rafa L.)

2018 ◽  
Vol 6 (2) ◽  
pp. 73
Author(s):  
Dewa Putu Yoga Gautama ◽  
I Made Anom S. Wijaya ◽  
I Wayan Widia
Keyword(s):  
Plant Growth ◽  
Plant Height ◽  
High Frequency ◽  
Dry Weight ◽  
Sound Waves ◽  
High Frequency Sound ◽  
Frequency Sound ◽  
Green Leaves ◽  
Mustard Plant ◽  
Canopy Area

Pemberian gelombang suara dengan frekuensi tinggi dapat merangsang mulut daun  (stomata) tetap terbuka, akibatnya laju dan efisiensi penyerapan pupuk meningkat yang bermanfaat bagi tanaman. Hasil penggunaan sonic bloom pada tanaman adalah mampu menstimulir metabolisme sel-sel tanaman, sehingga terjadi peningkatan penyerapan nutrisi dan uap air lewat daun yang berpengaruh pada pertumbuhan dan produktivitas tanaman. Tujuan dari penelitian ini yaitu (1) untuk mengetahui pengaruh pemberian musik Gamelan Bali terhadap pertumbuhan dan produktivitas tanaman sawi pakcoy dan (2) untuk menentukan jenis musik Gamelan Bali yang memberikan pertumbuhan dan produktivitas sawi pakcoy yang terbaik. Penelitan ini menggunakan tanaman sawi pakcoy (Brassica Rafa L.).  Perlakuan yang diberikan  dalam penelitian adalah pemberian musik gamelan bali dengan nuansa musik yang berbeda. Perlakuan 1 menggunakan musik gamelan Angklung, Perlakuan 2 menggunakan musik gamelan Semarpagulingan dan Perlakuan 3 menggunakan musik gamelan Gong Kebyar. Data yang diperoleh dianalis ANOVA dengan program IBM SPSS 20. Variabel yang diamati yaitu tinggi tanaman, luas kanopi daun tanaman, tingkat kehijauan daun tanaman, dan berat kering. Hasil penelitian menunjukan bahwa pemberian musik gong kebyar menghasilkan nilai tertinggi pada variabel tinggi tanaman, luas kanopi daun, tingkat kehijauan daun, dan berat kering yang  masing menghasilkan nilai yaitu yaitu 29,98 cm, 1684 cm2, 186,79, dan 68,61 gr. Pemberian musik memberikan pengaruh yang positif dan berbeda nyata pada pertumbuhan tanaman sawi pakcoy. Semakin tinggi frekuensi musik yang diberikan maka semakin baik pertumbuhan tanaman sawi pakcoy yang dihasilkan.  High frequency sound waves can stimulate the mouth of leaf (stomata) remains opened.The stomata remains open leading to efficient absorption of fertilizer. The purposes of this research were (1) to find out the effect of Balinese instrument music on the growth and productivity of pakcoy mustard plant and (2) to determine the type of Balinese instrument music that gives the best growth and productivity of mustard pakcoy. The treatment of this research was the application of Balinese instrument music with different musical nuances for 3 hours. Treatment 1 was using Angklung instruments music, treatment 2 was using Semarpagulingan instrument music and treatment 3 using Gong Kebyar instrument music. The obtained data was analized by ANOVA with the IBM SPSS 20 program. The observed variables include plant height, canopy area of plant leaf, green leaves level and dry weight. The results showed that Gong Kebyar instrument music application produces the highest value of 29.98 on the height of the plant variables, the widest value of 1684 cm2  on the canopy area variables, the biggest value that is 68,61 gr on the dry weight variables and the largest value of 186.79 on the green leaves level variables. Balinese instrument music application effect to the growth of pakcoy mustard plant. The best plant growth was the plant with gong kebyar instrument music application from all observed variables.

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