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.

scholarly journals The dual-slope conversion improvement

2014 ◽  
Vol 11 (3) ◽  
pp. 351-363
Author(s):  
Radojle Radetic ◽  
Marijana Pavlov-Kagadejev ◽  
Nikola Milivojevic
Keyword(s):  
High Frequency ◽  
Frequency Noise ◽  
Good Resolution ◽  
Practical Realization ◽  
Digital Conversion ◽  
Low Frequencies ◽  
Analog To Digital ◽  
High Frequency Noise ◽  
Low Input ◽  
Analog To Digital Conversion

The dual-slope ADC (DSADC) is a type of analog-to-digital conversion with low input bandwidths. It is pretty slow, but its ability to reject high-frequency noise and fixed low frequencies such as 50 Hz or 60 Hz makes it useful in noisy industrial environments and applications. It provides very good resolution. For the practical measurements in the Institutes laboratory an instrument is designed and realized. The base DSADC method is used, but improved by multiple conversions to make the measuring more precise and the time shorter. The special attention is paid to the problems occurred in practical realization and the way to overcome them. The paper describes the proposed and applied solutions, functional principles and achieved performances of the realized instrument.

scholarly journals Two-Mode Operation Engine Mount Design for Automotive Applications

2012 ◽  
Vol 19 (6) ◽  
pp. 1267-1280 ◽  
Author(s):  
Reza Tikani ◽  
Nader Vahdati ◽  
Saeed Ziaei-Rad
Keyword(s):  
Control Strategy ◽  
High Frequency ◽  
Frequency Noise ◽  
Automotive Applications ◽  
Low Frequencies ◽  
Engine Mounts ◽  
Mode Operation ◽  
Damping Characteristics ◽  
Engine Mount ◽  
Driving Condition

Hydraulic engine mounts are applied to the automotive applications to isolate the chassis from the high frequency noise and vibration generated by the engine as well as to limit the engine shake motions resulting at low frequencies. In this paper, a new hydraulic engine mount with a controllable inertia track profile is proposed and its dynamic behavior is investigated. The profile of the inertia track is varied by applying a controlled force to a cylindrical rubber disk, placed in the inertia track. This design provides a hydraulic engine mount design with an adjustable notch frequency location and also damping characteristics in shake motions. By using a simple control strategy, the efficiency of the proposed hydraulic engine mount in two-mode operation meaning isolating mode in the highway driving condition and damping mode in the shock motions, is investigated.

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.

scholarly journals Factors influencing low-frequency noise reduction in typical Chinese dwelling layouts

2020 ◽  
pp. 146134842094297
Author(s):  
Yang Song ◽  
Jian Kang
Keyword(s):  
Noise Reduction ◽  
Noise Exposure ◽  
Noise Source ◽  
Low Frequency ◽  
Frequency Noise ◽  
Low Frequency Noise ◽  
Low Frequencies ◽  
Factors Influencing ◽  
Polyline Distance

Existing approaches to reducing the low-frequency noise exposure of dwellings are not always sufficient. This study investigated the significance of dwelling layout design for low-frequency noise control. The sound distribution in six typical Chinese dwelling layouts was analysed using in-situ measurements under steady-state noise of various low frequencies. The results showed that among two-bedroom dwelling layouts, the overall average noise reduction varied considerably (6 dB). The noise reduction for room levels (number of rooms sound crosses) 1–2 and 2–3 varies by 5 and 3 dB, respectively, and the noise reduction at door openings varies by 5 dB. A model to approximate the low-frequency noise reduction of a layout was developed using the polyline distance from the noise source and the number of walls the polyline has to cross, which were clearly shown to influence low-frequency noise reduction and seem to be the strongest investigated factors.

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.

scholarly journals Aerofoil self-noise radiations subjected to serration flap angles

2021 ◽  
Vol 62 (7) ◽  
Author(s):  
P. C. Woodhead ◽  
T. P. Chong ◽  
P. F. Joseph ◽  
A. Vathylakis
Keyword(s):  
Noise Reduction ◽  
Flat Plate ◽  
High Frequency ◽  
Cross Flow ◽  
Broadband Noise ◽  
The Self ◽  
Spanwise Direction ◽  
Trailing Edge ◽  
Blade Loading ◽  
Loading Effect

Abstract Besides the investigation of the aeroacoustics responses of an asymmetric aerofoil subjected to serrated trailing edge flap angles from negative (flap-down) to positive (flap-up), this paper also provides a new perspective on the physical mechanisms of broadband noise reduction by a serrated trailing edge. The blade-loading effect, which is a function of the length and flap angle for a straight/non-serrated trailing edge flat plate, plays a considerable role in the self-noise radiation that is hitherto less recognised. When the same trailing edge flat plate is cut into a sawtooth serration shape, the self-noise reduction will be underpinned simultaneously by both the serration effect (dominant) and the blade-loading effect. The results demonstrate that the far-field radiation of a serrated aerofoil can be manipulated significantly depending on the direction of the flap angle. In the flap-down configuration, the blade-loading will become a negative factor that causes a deterioration of the noise reduction performance across the entire frequency range. In the flap-up configuration, three spectral frequencies zones can be defined. At the low-frequency zone, the diminished cross-flow at the sawtooth gaps will impede the noise reduction capability. At the central-frequency zone, the re-distribution of the turbulence sources and reduction in the turbulence spanwise length scales will enhance the noise reduction performance. Improvement in the noise performance can also be achieved at the high-frequency zone owing to the lack of interaction between the cross-flow and sawtooth structure. A new concept is positively demonstrated by varying the serration flap angle as a periodic function across the spanwise direction (spanwise wavy serration). When compared to a non-flap serrated trailing edge, the spanwise wavy serration is found to further increase the noise reduction level between the central and high-frequency regions. Graphic abstract

scholarly journals Applicability of Aeroacoustic Scaling Laws of Leading Edge Serrations for Rotating Applications

Acoustics ◽  
2020 ◽  
Vol 2 (3) ◽  
pp. 579-594 ◽  
Author(s):  
Till M. Biedermann ◽  
Pasquale Czeckay ◽  
Nils Hintzen ◽  
Frank Kameier ◽  
C. O. Paschereit
Keyword(s):  
Noise Reduction ◽  
Scaling Laws ◽  
Leading Edge ◽  
Broadband Noise ◽  
Geometrical Parameters ◽  
Destructive Interference ◽  
Turbulent Inflow ◽  
Leading Edges ◽  
Fan Blade ◽  
Inflow Conditions

The dominant aeroacoustic mechanisms of serrated leading edges, subjected to highly turbulent inflow conditions, can be compressed to spanwise decorrelation effects as well as effects of destructive interference. For single aerofoils, the resulting broadband noise reduction is known to follow spectral scaling laws. However, transferring serrated leading edges to rotating machinery, results in noise radiation patterns of significantly increased complexity, impeding to allocate the observed noise reduction to the underlying physical mechanisms. The current study aims at concatenating the scaling laws for stationary aerofoil and rotating-blade application and thus at providing valuable information on the aeroacoustic transferability of leading edge serrations. For the pursued approach, low-pressure axial fans are designed, obtaining identical serrated fan blade geometries than previously analyzed single aerofoils, hence allowing for direct comparison. Highly similar spectral noise reduction patterns are obtained for the broadband noise reduction of the serrated rotors, generally confirming the transferability and showing a scaling with the geometrical parameters of the serrations as well as the inflow conditions. Continuative analysis of the total noise reduction, however, constrains the applicability of the scaling laws to a specific operating range of the rotors and motivates for a devaluation of the scaling coefficients regarding additional rotor-specific effects.

Optimised Test Rig for Measurements of Aerodynamic and Aeroacoustic Performance of Leading Edge Serrations in Low-Speed Fan Application

2018 ◽  
Author(s):  
Till M. Biedermann ◽  
F. Kameier ◽  
C. O. Paschereit
Keyword(s):  
Noise Reduction ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Broadband Noise ◽  
Test Rig ◽  
Low Speed ◽  
Turbulent Inflow ◽  
Inflow Turbulence ◽  
Leading Edges ◽  
Inflow Conditions

With the aim of analysing the efficiency of leading edge serrations under realistic conditions, an experimental rig was developed where a ducted low-speed fan is installed that allows to gather data of both, aerodynamic and aeroacoustic nature. Turbulent inflow conditions were generated via biplane-square grids, resulting in turbulence intensities of different magnitude and of high isotropic character that were quantified by use of hotwire measurements. The fan blades were designed according to the NACA65(12)-10 profile with interchangeable features and an independently adjustable angle of attack. Altogether, five different parameters can be analysed, namely the serration amplitude and wavelength, the angle of attack, the inflow turbulence and the rotational speed. In addition, the blade design allows for a variation of the blade skew, sweep and dihedral as well. The presented work focusses on validating and optimising the test rig as well as a detailed quantification of the turbulent inflow conditions. Furthermore, first aerodynamic and aeroacoustic results of fan blades with straight leading edges are compared to those of serrated leading edges. The aerodynamic performance was found to be mainly affected by the serrations as a function of the serration amplitude. Aeroacoustically, a clear sensitivity towards different incoming turbulence intensities and serration parameters was detected, showing significant broadband noise reduction below 2 kHz with an overall noise reduction of ΔOASPL = 3.4 dB at maximum serration amplitudes and minimum wavelengths.

scholarly journals Numerical analysis of a 3-D printed porous trailing edge for broadband noise reduction

2021 ◽  
Vol 926 ◽  
Author(s):  
C. Teruna ◽  
F. Avallone ◽  
D. Ragni ◽  
A. Rubio-Carpio ◽  
D. Casalino
Keyword(s):  
Noise Reduction ◽  
High Frequency ◽  
Dominant Role ◽  
Broadband Noise ◽  
Excess Noise ◽  
Entrance Length ◽  
Noise Mitigation ◽  
Trailing Edge ◽  
Turbulent Length Scale ◽  
Porous Insert

Lattice Boltzmann simulations were carried out to investigate the noise mitigation mechanisms of a 3-D printed porous trailing-edge insert, elucidating the link between noise reduction and material permeability. The porous insert is based on a unit cell resembling a lattice of diamond atoms. It replaces the last 20 % chord of a NACA 0018 at zero angle-of-attack. A partially blocked insert is considered by adding a solid partition between 84 % and 96 % of the aerofoil chord. The regular porous insert achieves a substantial noise reduction at low frequencies, although a slight noise increase is found at high frequencies. The partially blocked porous insert exhibits a lower noise reduction level, but the noise emission at mid-to-high frequency is slightly affected. The segment of the porous insert near the tip plays a dominant role in promoting noise mitigation, whereas the solid-porous junction contributes, in addition to the rough surface, towards the high-frequency excess noise. The current study demonstrates the existence of an entrance length associated with the porous material geometry, which is linked to the pressure release process that is responsible for promoting noise mitigation. This process is characterised by the aerodynamic interaction between pressure fluctuations across the porous medium, which is found at locations where the porous insert thickness is less than twice the entrance length. Present results also suggest that the noise attenuation level is related to both the chordwise extent of the porous insert and the streamwise turbulent length scale. The porous inserts also cause a slight drag increase compared to their solid counterpart.

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