Experimental Analysis for Jet Noise Reduction of Chevron Pylon-Based Nozzles

The experimental analysis is conducted for jet noise reduction of separate flow chevron pylon-based nozzles at takeoff condition. The experimental results indicate that the pylon makes a noise reduction at low-frequency but produces an increase at high-frequency, together with an overall sound pressure reduction below the pylon. Compared to chevron nozzle without pylon, the adding of a pylon reduces noise benefit of chevron nozzles found in the isolated nozzle without a pylon. The best low-frequency noise reduction is located below the pylon where peak noise reduction is as high as about 1.3dB on frequency spectrum.

Download Full-text

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

International Journal of Aeroacoustics ◽

10.1177/1475472x20978388 ◽

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.

Download Full-text

Noise-silencing technology for upright venting pipe jet noise

Advances in Mechanical Engineering ◽

10.1177/1687814018794819 ◽

2018 ◽

Vol 10 (8) ◽

pp. 168781401879481 ◽

Cited By ~ 5

Author(s):

Enbin Liu ◽

Shanbi Peng ◽

Tiaowei Yang

Keyword(s):

Natural Gas ◽

Sound Pressure Level ◽

Sound Pressure ◽

Low Frequency ◽

Jet Noise ◽

Pressure Level ◽

Living Environment ◽

Frequency Noise ◽

Frequency Range ◽

Expansion Chamber

When a natural gas transmission and distribution station performs a planned or emergency venting operation, the jet noise produced by the natural gas venting pipe can have an intensity as high as 110 dB, thereby severely affecting the production and living environment. Jet noise produced by venting pipes is a type of aerodynamic noise. This study investigates the mechanism that produces the jet noise and the radiative characteristics of jet noise using a computational fluid dynamics method that combines large eddy simulation with the Ffowcs Williams–Hawkings acoustic analogy theory. The analysis results show that the sound pressure level of jet noise is relatively high, with a maximum level of 115 dB in the low-frequency range (0–1000 Hz), and the sound pressure level is approximately the average level in the frequency range of 1000–4000 Hz. In addition, the maximum and average sound pressure levels of the noise at the same monitoring point both slightly decrease, and the frequency of the occurrence of a maximum sound pressure level decreases as the Mach number at the outlet of the venting pipe increases. An increase in the flow rate can result in a shift from low-frequency to high-frequency noise. Subsequently, this study includes a design of an expansion-chamber muffler that reduces the jet noise produced by venting pipes and an analysis of its effectiveness in reducing noise. The results show that the expansion-chamber muffler designed in this study can effectively reduce jet noise by 10–40 dB and, thus, achieve effective noise prevention and control.

Download Full-text

Theoretical End Experimental Evaluation of Perforations Effect on Sound Insulation

Proccedings of 10th International Conference "Environmental Engineering" ◽

10.3846/enviro.2017.027 ◽

2017 ◽

Author(s):

Olga Khrystoslavenko ◽

Raimondas Grubliauskas

Keyword(s):

Noise Reduction ◽

High Frequency ◽

Sound Absorption ◽

Low Frequency ◽

Experimental Methods ◽

Glass Wool ◽

Acoustic Properties ◽

Sound Insulation ◽

Frequency Noise ◽

Sound Reduction

To design a sound-absorbing panel, it is important to identify factors that affect the maximum sound absorption of low, middle and high frequency sounds. Perforation effect is very important for the noise-reducing and noiseabsorbing panels. Perforations are often used for sound reduction. Experimental data shows that the perforation is very effective to absorb low-frequency noise. In the presented study, influence of perforation coefficient of noise reduction was analyzed with theoretical and experimental methods. The experiments were conducted in noise reduction chamber using an perforated construction with glass wool filler. Sound reductions index of 15 dB indicates good acoustic properties of the panel.

Download Full-text

An experimental study of the effects of lobed nozzles on installed jet noise

Experiments in Fluids ◽

10.1007/s00348-019-2819-x ◽

2019 ◽

Vol 60 (12) ◽

Cited By ~ 1

Author(s):

Benshuai Lyu ◽

Ann P. Dowling

Keyword(s):

Noise Reduction ◽

High Frequency ◽

Jet Noise ◽

Intermediate Frequency ◽

Dominant Mode ◽

Frequency Noise ◽

Mean Flow ◽

Instability Waves ◽

Jet Mixing ◽

Jet Instability

Abstract Jet noise remains a significant aircraft noise contributor, and for modern high-bypass-ratio aero-engines the strong interaction between the jet and aircraft wing leads to intensified installed jet noise. An experiment is carried out in this paper to study the effects of lobed nozzles on installed jet noise. It is found that the lobed nozzles, compared to round nozzles, have similar effects on installed jet noise for all the plate positions and Mach numbers tested. On the shielded side of the plate, the use of lobed nozzles leads to a noise reduction in the intermediate- and high-frequency regimes, which is thought to be due to a combination of enhanced jet mixing and more effective shielding effects by the flat plate. On the reflected side of the plate, noise reduction is only achieved in the intermediate frequency range; the little noise reduction or a slight noise increase observed in the high-frequency regime is likely due to enhanced jet mixing. On both sides of the plates, little noise reduction is achieved for the low-frequency noise due to the scattering of jet instability waves. This is likely to be caused by the fact that lobed nozzles cause negligible change to the dominant mode 0 (axisymmetric) jet instability waves. That the jet mean flow quickly becomes axisymmetric downstream of the jet exit could also play a role. Graphic abstract

Download Full-text

Study of Sound Insulation of Control Cabins in Industry in the Low Frequency Range

Journal of Low Frequency Noise Vibration and Active Control ◽

10.1177/026309239201100202 ◽

1992 ◽

Vol 11 (2) ◽

pp. 42-46

Author(s):

Anna Kaczmarska ◽

Danuta Augustyriska

Keyword(s):

Noise Reduction ◽

Sound Pressure ◽

Low Frequency ◽

Machine Building ◽

Sound Insulation ◽

Frequency Noise ◽

Low Frequency Noise ◽

Frequency Range ◽

Sound Pressure Levels ◽

Lower Frequencies

The number of control cabins installed in industry has increased considerably during the last few years. Most cabins installed nowadays show a satisfactory noise reduction in the frequency range above 500 Hz. The effect of noise damping however shows a gradual decrease for lower frequencies. The present paper is a description of the distribution of low frequency noise in different types of control cabins installed in typical low frequency noise environments in steel plants and the machine building industry. Measurements were made in 20 control cabins, constructed of metal and stone Measurements of sound pressure levels in octave bands were made inside and outside the cabins. The sound pressure level in octave bands in the low frequency range (4–31.5 Hz) inside the cabins was high and varied between 60–108 dB. This is probably due to the insufficient noise reduction for lower frequencies. In some control cabins there was an increased level of low frequency noise inside the cabin compared to the outside. In these control cabins sound pressure levels exceed the admissible values according to Polish standards. The increase of noise level within the low frequency range is considered to be based on resonances.

Download Full-text

Numerical Simulation of Noise Radiation from Semi-Hermetic Reciprocating Food Refrigeration Compressors

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.248.85 ◽

2012 ◽

Vol 248 ◽

pp. 85-90

Author(s):

Li Zhang ◽

Yuan Yuan Zhang ◽

Yan Miao Ma

Keyword(s):

Numerical Simulation ◽

Noise Reduction ◽

Sound Pressure ◽

Negative Impact ◽

Low Frequency ◽

Radiation Energy ◽

Frequency Noise ◽

Noise Radiation ◽

Piston Cylinder ◽

Virtual Lab

The semi-hermetic reciprocating compressor is the dominant noise source of food refrigeration unit. Excessive noise and vibration have a negative impact on both people's health and work efficiency；moreover, it causes fatigue damage to machinery thus reducing its working life. In this paper, numerical simulation of noise radiation from semi-hermetic reciprocating food refrigeration was carried out by successful combination of Pro/E, Hypermesh, Nastran and Virtual Lab Acoustics software. The simulation results show that the low-frequency noise radiation near the end of the piston-cylinder is directional and stronger than that of the other side, which offers a valuable reference for noise reduction. In addition, the sound pressure dB curve of any field point can be obtained through the numerical simulation, and it clearly shows that sound pressure values away from the piston end are significantly lower than those at the piston side; and noise radiation energy of compressor concentrates at 500Hz and 1000Hz. This paper provides an effective research method for the semi-hermetic reciprocating compressor’s noise reduction

Download Full-text

Real Ear Sound Pressure Levels Developed by Three Portable Stereo System Earphones

American Journal of Audiology ◽

10.1044/1059-0889.0104.52 ◽

1992 ◽

Vol 1 (4) ◽

pp. 52-55 ◽

Cited By ~ 4

Author(s):

Gail L. MacLean ◽

Andrew Stuart ◽

Robert Stenstrom

Keyword(s):

High Frequency ◽

Sound Pressure ◽

Low Frequency ◽

Test System ◽

Output Frequency ◽

Frequency Effects ◽

Adult Men ◽

Frequency Responses ◽

Significant Difference ◽

Sound Pressure Levels

Differences in real ear sound pressure levels (SPLs) with three portable stereo system (PSS) earphones (supraaural [Sony Model MDR-44], semiaural [Sony Model MDR-A15L], and insert [Sony Model MDR-E225]) were investigated. Twelve adult men served as subjects. Frequency response, high frequency average (HFA) output, peak output, peak output frequency, and overall RMS output for each PSS earphone were obtained with a probe tube microphone system (Fonix 6500 Hearing Aid Test System). Results indicated a significant difference in mean RMS outputs with nonsignificant differences in mean HFA outputs, peak outputs, and peak output frequencies among PSS earphones. Differences in mean overall RMS outputs were attributed to differences in low-frequency effects that were observed among the frequency responses of the three PSS earphones. It is suggested that one cannot assume equivalent real ear SPLs, with equivalent inputs, among different styles of PSS earphones.

Download Full-text