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

2019 ◽  
Vol 60 (12) ◽  
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

scholarly journals Modelling installed jet noise due to the scattering of jet instability waves by swept wings

2019 ◽  
Vol 870 ◽  
pp. 760-783 ◽  
Author(s):  
Benshuai Lyu ◽  
Ann P. Dowling
Keyword(s):  
Noise Reduction ◽  
Physical Mechanism ◽  
Jet Noise ◽  
Destructive Interference ◽  
Sweep Angle ◽  
Low Frequencies ◽  
Instability Waves ◽  
Jet Instability ◽  
Reduction Strategies ◽  
Swept Wings

Jet noise is a significant contributor to aircraft noise, and on modern aircraft it is considerably enhanced at low frequencies by a closely installed wing. Recent research has shown that this noise increase is due to the scattering of jet instability waves by the trailing edge of the wing. Experimentalists have recently shown that noise can be reduced by using wings with swept trailing edges. To understand this mechanism, in this paper, we develop an analytical model to predict the installed jet noise due to the scattering of instability waves by a swept wing. The model is based on the Schwarzschild method and Amiet’s approach is used to obtain the far-field sound. The model can correctly predict both the reduction in installed jet noise and the change to directivity patterns observed in experiments due to the use of swept wings. The agreement between the model and experiment is very good, especially for the directivity at large azimuthal angles. It is found that the principal physical mechanism of sound reduction is due to destructive interference. It is concluded that in order to obtain an effective noise reduction, both the span and the sweep angle of the wing have to be large. Such a model can greatly aid in the design of quieter swept wings and the physical mechanism identified can provide significant insight into developing other innovative noise-reduction strategies.

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

2014 ◽  
Vol 1078 ◽  
pp. 183-186 ◽  
Author(s):  
Jing Yu He ◽  
Ying Bo Xu
Keyword(s):  
Noise Reduction ◽  
Experimental Analysis ◽  
High Frequency ◽  
Sound Pressure ◽  
Low Frequency ◽  
Jet Noise ◽  
Separate Flow ◽  
Frequency Noise ◽  
Chevron Nozzle ◽  
Chevron 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.

scholarly journals On the universal trends in the noise reduction due to wavy leading edges in aerofoil–vortex interaction

2019 ◽  
Vol 871 ◽  
pp. 186-211 ◽  
Author(s):  
Jacob M. Turner ◽  
Jae Wook Kim
Keyword(s):  
Noise Reduction ◽  
High Frequency ◽  
Broadband Noise ◽  
Current Work ◽  
Source Distribution ◽  
Source Analysis ◽  
Frequency Noise ◽  
Frequency Spectra ◽  
Low Frequencies ◽  
Leading Edges

Existing studies suggest that wavy leading edges (WLEs) offer substantial reduction of broadband noise generated by an aerofoil undergoing upstream vortical disturbances. In this context, there are two universal trends in the frequency spectra of the noise reduction which have been observed and reported to date: (i) no significant reduction at low frequencies followed by (ii) a rapid growth of the noise reduction that persists in the medium-to-high frequency range. These trends are known to be insensitive to the aerofoil type and flow condition used. This paper aims to provide comprehensive understandings as to how these universal trends are formed and what the major drivers are. The current work is based on very-high-resolution numerical simulations of a semi-infinite flat-plate aerofoil impinged by a prescribed divergence-free vortex in an inviscid base flow at zero incidence angle, continued from recent work by the authors (Turner & Kim, J. Fluid Mech., vol. 811, 2017, pp. 582–611). One of the most significant findings in the current work is that the noise source distribution on the aerofoil surface becomes entirely two-dimensional (highly non-uniform in the spanwise direction as well as streamwise) at high frequencies when the WLE is involved. Also, the sources downstream of the LE make crucial contributions to creating the universal trends across all frequencies. These findings contradict the conventional LE-focused one-dimensional source analysis that has widely been accepted for all frequencies. The current study suggests that the universal trends in the noise-reduction spectra can be properly understood by taking the downstream source contributions into account, in terms of both magnitude and phase variations. After including the downstream sources, it is shown in this paper that the first universal trend is due to the conservation of total (surface integrated) source energy at low frequencies. The surface-integrated source magnitude that decreases faster with the WLE correlates very well with the noise-reduction spectrum at medium frequencies. In the meantime, the high-frequency noise reduction is driven almost entirely by destructive phase interference that increases rapidly and consistently with frequency, explaining the second universal trend.

Car's Materials Acoustic Properties Test and Analysis

2013 ◽  
Vol 785-786 ◽  
pp. 1244-1247
Author(s):  
Yan Liu ◽  
Xiao Juan Zhang ◽  
Zong Cai Liu
Keyword(s):  
Noise Reduction ◽  
High Frequency ◽  
Sound Absorption ◽  
Transmission System ◽  
Acoustic Properties ◽  
Frequency Noise ◽  
Car Industry ◽  
High Frequency Noise ◽  
Urban Construction ◽  
The Impact

With the development of the car industry, the pace of the urban construction is accelerating as well. Cars have gradually entered the ordinary family. As the car noise has a big effect on the health of the passengers, as well as on the surroundings, one of the car industry key duties is the car noise reduction. By researching the materials applied to car, this article describe that PU material could reduce the impact of the engine noise on the cab efficiently; Polypropylene needle-spun felt could reduce the noise passed by chassis; PET material's sound absorption is poor in mid bass, however in high frequency it's sound absorption is good; sound absorbing sponge can reduce the low and high frequency noise; The combine sponge can reduce the noise from the tire and transmission system ; Cotton material could absorb the high frequency noise.

The Influence of Climatic Factors on the Distribution of Noise from Gas Distribution Stations

Vestnik MEI ◽  
2020 ◽  
Vol 5 (5) ◽  
pp. 79-83
Author(s):  
Vladimir B. Tupov ◽  
◽  
Vitaliy S. Skvortsov ◽  
Keyword(s):  
Noise Reduction ◽  
High Frequency ◽  
Climatic Factors ◽  
Frequency Noise ◽  
Octave Band ◽  
City Region ◽  
Gas Distribution ◽  
Central Frequency ◽  
High Frequency Noise ◽  
Maximum Range

The article discusses the influence of regional climatic factors on the propagation of noise from gas distribution stations (GDS), which are intense sources of noise for the surrounding area, and suggests a procedure for determining the required extent of noise reduction. GDSs produce high-frequency noise with the maximum values at the octave band central frequencies equal to 1000, 2000, 4000, and 8000 Hz. It is shown that climatic factors have quite a significant influence on the propagation of high-frequency noise from gas distribution stations precisely at the octave band central frequencies equal to 1000, 2000, 4000, 8000 Hz. The sound pressure levels may vary very significantly during a year depending on the region due to sound attenuation factors in the atmosphere. The climatic data for 210 cities of Russia were analyzed. The data on variation of climatic conditions during a year for these cities are taken from the Code SP 131.13330.2012. These changes for the octave band central frequency equal to 4000 Hz can make from the minimum range of 5.61 dB in the Sochi city region to the maximum range of 19.35 dB in the Chita city region; for the octave band central frequency equal to 8000 Hz they can make from the minimum range of 14.58 dB in the Elton city region to the maximum range of 48.63 dB in the Chita city region. The difference between the range smallest and largest values increases with the octave band central frequency. Thus, for the octave band central frequency equal to 1000 Hz this difference is 3 dB, whereas for the octave band central frequency equal to 8000 Hz this difference is 34 dB. The influence of climatic factors on the required extent of noise reduction from a GDS depends significantly on the region and can make tens of decibels for a combined heat and power plant with a 300-m wide sanitary protection zone. Therefore, for elaborating the necessary measures for reducing noise from a GDS, it is necessary to take into account the minimum atmospheric sound absorption coefficient for a particular region.

scholarly journals Noise reduction through joint processing of gravity and gravity gradient data

Geophysics ◽  
2008 ◽  
Vol 73 (3) ◽  
pp. I23-I34 ◽  
Author(s):  
G. Pajot ◽  
O. de Viron ◽  
M. Diament ◽  
M.-F. Lequentrec-Lalancette ◽  
V. Mikhailov
Keyword(s):  
Noise Reduction ◽  
High Frequency ◽  
Random Noise ◽  
Gravity Gradient ◽  
Small Scale ◽  
Frequency Noise ◽  
Gravity Gradiometry ◽  
Physical Constraints ◽  
Simultaneous Inversion ◽  
Marine Gravity

In mineral and oil exploration, gravity gradient data can help to delineate small-scale features that cannot be retrieved from gravity measurements. Removing high-frequency noise while preserving the high-frequency real signal is one of the most challenging tasks associated with gravity gradiometry data processing. We present a method to reduce gravity and gravity gradient data noise when both are measured in the same area, based on a least-squares simultaneous inversion of observations and physical constraints, inferred from the gravity gradient tensor definition and its mathematical properties. Instead of handling profiles individually, our noise-reduction method uses simultaneously measured values of the tensor components and of gravity in the whole survey area, benefiting from all available information. Synthetic examples show that more than half of the random noise can be removed from all tensor components and nearly all the noise from the gravity anomaly without altering the high-frequency information. We apply our method to a set of marine gravity gradiometry data acquired by Bell Geospace in the Faroe-Shetland Basin to demonstrate its power to resolve small-scale features.

Theoretical End Experimental Evaluation of Perforations Effect on Sound Insulation

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.

Hot-Jet Noise Test of a Revised Notched Nozzle

2012 ◽  
Author(s):  
Tatsuya Ishii ◽  
Nozomi Tanaka ◽  
Hideshi Oinuma ◽  
Tsutomu Oishi
Keyword(s):  
Noise Reduction ◽  
Flow Rate ◽  
High Speed ◽  
Large Scale ◽  
Jet Noise ◽  
Outdoor Environment ◽  
Engine Test ◽  
Noise Component ◽  
Jet Mixing ◽  
Noise Test

Jet noise remains a significant noise component in modern commercial aero-engines. A high-speed flow mixing with the surrounding air constitutes noise sources behind the nozzle. One noise-reduction technology is a mixing device attached to the nozzle. Several fixed-geometry mixers such as chevrons have been studied by both computational and experimental approaches. The authors have previously proposed a notched nozzle with dents allocated along the nozzle lip and discussed its ability to reduce the noise level. The revised notch was expected to suppress the broadband jet-mixing noise as well as additional noise at higher frequencies. However, further assessments are required before proceeding to a large-scale engine test in an outdoor environment. First, the influence of the gas temperature on acoustic results must be tested because the temperature affects the mean jet velocity and sound propagation. As the preliminary noise test in the previous paper was limited to the cold-jet condition, far-field noise data under the hot-jet condition should be investigated. Second, the aerodynamic performance must be evaluated. Data on the flow rate and thrust would help in considering the aerodynamic performances between the baseline, notched, and chevron nozzles. This study focuses on noise tests for the finer-notched nozzle under the hot-gas condition. A small jet engine for model jet planes was employed to generate a high-temperature jet. An engine test stand was designed to monitor the engine performance data, consisting of the pressure and temperature at several positions, the fuel flow rate, and the thrust. The hot-jet test with and without the mixing device served as a compact and flexible test for aerodynamic evaluation of the nozzle. The noise test results under the hot-jet condition with this rig showed that the noise reduction characteristics of the finer-notched nozzle are different from those of conventional mixers.

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