scholarly journals 3D Acoustic Modelling of Dissipative Silencers with Nonhomogeneous Properties and Mean Flow

2014 ◽  
Vol 6 ◽  
pp. 537935 ◽  
Author(s):  
E. M. Sánchez-Orgaz ◽  
F. D. Denia ◽  
J. Martínez-Casas ◽  
L. Baeza
Keyword(s):  
Bulk Density ◽  
Acoustic Analysis ◽  
Sound Propagation ◽  
Transmission Loss ◽  
Acoustic Properties ◽  
Mean Flow ◽  
Absorbent Material ◽  
Outer Chamber ◽  
Nonhomogeneous Properties ◽  
Flow Effects

A finite element approach is proposed for the acoustic analysis of automotive silencers including a perforated duct with uniform axial mean flow and an outer chamber with heterogeneous absorbent material. This material can be characterized by means of its equivalent acoustic properties, considered coordinate-dependent via the introduction of a heterogeneous bulk density, and the corresponding material airflow resistivity variations. An approach has been implemented to solve the pressure wave equation for a nonmoving heterogeneous medium, associated with the problem of sound propagation in the outer chamber. On the other hand, the governing equation in the central duct has been solved in terms of the acoustic velocity potential considering the presence of a moving medium. The coupling between both regions and the corresponding acoustic fields has been carried out by means of a perforated duct and its acoustic impedance, adapted here to include absorbent material heterogeneities and mean flow effects simultaneously. It has been found that bulk density heterogeneities have a considerable influence on the silencer transmission loss.

Swirling mean flow effects on locally reacting interstage liner

2021 ◽  
pp. 1475472X2110433
Author(s):  
Vianney Masson ◽  
Stéphane Moreau ◽  
Hélène Posson ◽  
Thomas Node-Langlois
Keyword(s):  
Transmission Loss ◽  
Axial Flow ◽  
Matrix Formalism ◽  
Transmission Losses ◽  
Mean Flow ◽  
Azimuthal Mode ◽  
Total Enthalpy ◽  
Flow Effects ◽  
Small Rotation ◽  
Mode Order

Sound transmission through a finite-lined section in a rigid annular duct with swirling and sheared mean flow is analyzed with a new mode-matching method based on the conservation of the total enthalpy and the mass flow, which does not reduce to the conservation of the pressure and the axial velocity when the swirl is non-zero. It relies on a new projection method based on the property of the Chebyshev polynomials and on the scattering matrix formalism to yield transmission losses. This new method is first validated against a finite elements method tool in the uniform axial flow case, and then provides a parametric study of the effect of swirl. At low azimuthal mode order [Formula: see text], the swirl amplifies the attenuation of the contra-rotating modes and makes the attenuation of the co-rotating modes decrease with a trend of a general shift of the transmission loss curve toward contra-rotating modes. A small rotation of the transmission loss curves at low [Formula: see text] is also generally observed. The boundary condition in the lined section has a small effect on the transmission loss, except close to the cut-on thresholds. Finally, the duct boundary-layer thickness has a significant effect on the cut-on modes and the transmission loss but not its profile.

Acoustic Modeling of Charge Air Coolers

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Magnus Knutsson ◽  
Mats Åbom
Keyword(s):  
Gas Exchange ◽  
Sound Propagation ◽  
Transmission Loss ◽  
Sound Transmission ◽  
Acoustic Properties ◽  
Passenger Cars ◽  
Air Intake ◽  
Ic Engines ◽  
Reactive Properties ◽  
Good Agreement

The necessity of reducing CO2 emissions has lead to an increased number of passenger cars that utilize turbocharging to maintain performance when the internal combustion (IC) engines are downsized. Charge air coolers (CACs) are used on turbocharged engines to enhance the overall gas exchange efficiency. Cooling of charged air increases the air density and thus the volumetric efficiency and also increases the knock margin (for petrol engines). The acoustic properties of charge coolers have so far not been extensively treated in the literature. Since it is a large component with narrow flow passages, it includes major resistive as well as reactive properties. Therefore, it has the potential to largely affect the sound transmission in air intake systems and should be accurately considered in the gas exchange optimization process. In this paper, a frequency domain acoustic model of a CAC for a passenger car is presented. The cooler consists of two conical volumes connected by a matrix of narrow ducts where the cooling of the air takes place. A recently developed model for sound propagation in narrow ducts that takes into account the attenuation due to thermoviscous boundary layers and interaction with turbulence is combined with a multiport representation of the tanks to obtain an acoustic two-port representation where flow is considered. The predictions are compared with experimental data taken at room temperature and show good agreement. Sound transmission loss increasing from 5 to over 10 dB in the range 50–1600 Hz is demonstrated implying good noise control potential.

The influence of mean flow on the acoustic properties of a tube bank

1984 ◽  
Vol 396 (1811) ◽  
pp. 383-403 ◽  
Keyword(s):  
Dispersion Equation ◽  
Sound Propagation ◽  
Circular Cross Section ◽  
Cross Flow ◽  
Acoustic Properties ◽  
Mean Flow ◽  
Tube Bank ◽  
Conservation Of Energy ◽  
Trailing Edges ◽  
The Mean

The theory of sound propagation through a bank of rigid parallel tubes in the presence of a nominally steady, low Mach number cross flow is discussed. A detailed diffraction analysis is given for the idealized but mathematically tractable case of a bank of strips set at zero angle of attack to the mean flow. Various approximations for the dispersion equation governing the propagation of long waves are derived, including the influence of acoustically induced vortex shedding from the strip trailing edges and of hydrodynamic interactions between neighbouring strips. The sound is attenuated by a transfer of energy to the kinetic energy of the essentially incompressible field of the shed vorticity. It is shown how the principle of conservation of energy and a Kramers-Kronig dispersion relation can be combined to yield an alternative derivation of the dispersion equation. This procedure is applicable to a simplified model of propagation through a bank of rigid tubes of circular cross section, and an approximation to the dispersion equation is obtained in this case. The relevance of these results to bound resonances in tube bank cavities is discussed.

scholarly journals Effect of Subsurface Mediterranean Water Eddies on Sound Propagation Using ROMS Output and the Bellhop Model

Water ◽  
2021 ◽  
Vol 13 (24) ◽  
pp. 3617
Author(s):  
Seyed Hossein Hassantabar Bozroudi ◽  
Daniele Ciani ◽  
Mahdi Mohammad Mahdizadeh ◽  
Mohammad Akbarinasab ◽  
Ana Claudia Barbosa Aguiar ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
Sound Propagation ◽  
Transmission Loss ◽  
Acoustic Energy ◽  
Acoustic Properties ◽  
Angular Distributions ◽  
Northeastern Atlantic Ocean ◽  
Mediterranean Water ◽  
Northeastern Atlantic

Ocean processes can locally modify the upper ocean density structure, leading to an attenuation or a deflection of sound signals. Among these phenomena, eddies cause significant changes in acoustic properties of the ocean; this suggests a possible characterization of eddies via acoustics. Here, we investigate the propagation of sound signals in the Northeastern Atlantic Ocean in the presence of eddies of Mediterranean Water (Meddies). Relying on a high-resolution simulation of the Atlantic Ocean in which Meddies were identified and using the Bellhop acoustic model, we investigated the differences in sound propagation in the presence and absence of Meddies. Meddies create sound channels in which the signals travel with large acoustic energy. The transmission loss decreases to 80 or 90 dB; more signals reach the synthetic receivers. Outside of these channels, the sound signals are deflected from their normal paths. Using receivers at different locations, the acoustic impact of different Meddies, or of the same Meddy at different stages of its life, are characterized in terms of angular distributions of times of arrivals and of energy at reception. Determining the influence of Meddies on acoustic wave characteristics at reception is the first step to inverting the acoustic signals received and retrieving the Meddy hydrological characteristics.

Acoustic Analysis of a Liquid Fuel Swirl Combustor Using Dynamic Mode Decomposition

2015 ◽  
Author(s):  
Abdulla Ghani ◽  
Laurent Gicquel ◽  
Thierry Poinsot
Keyword(s):  
Acoustic Analysis ◽  
Dynamic Mode Decomposition ◽  
Dynamic Mode ◽  
Mean Flow ◽  
Swirl Combustor ◽  
Eddy Simulation ◽  
Mode Decomposition ◽  
Flame Response ◽  
Unstable Combustion ◽  
Flow Effects

The flame transfer function (FTF) of an aeronautical burner in a rectangular combustion chamber is determined using large eddy simulation (LES). The configuration contains an industrial swirling device placed in a laboratory combustor. The swirler comprises three air passages and liquid kerosene is injected through a pilot and a multipoint injection device including 24 injection holes. In order to reduce computational costs, the forcing process for FTF determination is limited to three forcing cycles. Application of the dynamic mode decomposition (DMD) allows to extract the coherent flow structures at the forcing frequency and to construct local flame response and time delay fields. In a next step, modal analysis is carried out with a Helmholtz solver where acoustic boundary conditions are utilized taking mean flow effects into account. The latter allows to model mean flow effects in a zero Mach number framework. Results are compared with experimental observations: stable and unstable combustion modes for different outlet impedances are correctly identified by this methodology. All results are validated against experimental data and show good agreement.

scholarly journals Effect of Flow on Various Helmholtz Resonators

2020 ◽  
Vol 25 (1) ◽  
pp. 73-78
Author(s):  
Hyunsu Kim ◽  
Iljae Lee
Keyword(s):  
Transmission Loss ◽  
Flow Conditions ◽  
Mean Flow ◽  
Direct Flow ◽  
Acoustic Performance ◽  
Helmholtz Resonators ◽  
Flow Impedance ◽  
Flow Effects ◽  
Two Peaks ◽  
The Impact

The acoustic performance of Helmholtz resonators with different configurations in the presence of mean flow is experimentally investigated. The transmission loss of Helmholtz resonators is measured using a flow-impedance tube setup to identify mean flow effects. First, Helmholtz resonators under two different flow conditions, grazing and direct flow, are considered at Ma=0.05 and 0.1. Then the impact of mean flow on the transmission loss of Helmholtz resonators with leakage holes is also demonstrated. For Helmholtz resonators with leakage holes, single peak of transmission loss is identified at Ma=0.0 and 0.1. However, two peaks appear at Ma=0.05 as the number of opening holes increases. The experimental results show that the effect of mean flow strongly depends on the configurations of Helmholtz resonators and the conditions of mean flow. Thus the variation of acoustic performance due to mean flow should be considered in the design of Helmholtz resonators.

The acoustics of turbulence near sound-absorbent liners

1972 ◽  
Vol 51 (4) ◽  
pp. 737-749 ◽  
Author(s):  
John E. Ffowcs Williams
Keyword(s):  
Acoustic Properties ◽  
Plane Boundary ◽  
Fourth Power ◽  
Small Scale ◽  
Generation Process ◽  
Mean Flow ◽  
Acoustic Liners ◽  
Rigid Plane ◽  
Flow Effects ◽  
Scale Turbulence

Acoustic liners are often perforated screens backed by sound-absorbent material. Turbulence can interact with these screens to generate additional sound. The dynamics of the generation process is examined in this paper, where the liner is modelled as an infinite rigid plane boundary with a homogeneous array of circular orifices or rigid pistons. The acoustic properties of these boundaries are derived in the long wavelength limit. Small-scale turbulence is scattered by individual apertures into sound. Acoustically transparent surfaces support dipole scattering centres while more ‘opaque’ surfaces have monopoles at the apertures which convert turbulence into sound more effectively. It is shown that the process can be described once the response of an individual aperture in an infinite baffle is known. At low Mach numbers the screen can increase the sound radiated by adjacent turbulence by a factor equal to the inverse fourth power of the Mach number. Mean-flow effects are ignored but they are thought to increase the effects deduced in this preliminary study.

Effect of leakage and blockage on the acoustic behavior of particle filters

2019 ◽  
Vol 67 (6) ◽  
pp. 483-492
Author(s):  
Seonghyeon Baek ◽  
Iljae Lee
Keyword(s):  
Transfer Matrix ◽  
Particle Filters ◽  
Acoustic Analysis ◽  
Transmission Loss ◽  
One Dimensional ◽  
Filter System ◽  
The Difference ◽  
The One ◽  
Analytical Approaches ◽  
Good Agreement

The effects of leakage and blockage on the acoustic performance of particle filters have been examined by using one-dimensional acoustic analysis and experimental methods. First, the transfer matrix of a filter system connected to inlet and outlet pipes with conical sections is measured using a two-load method. Then, the transfer matrix of a particle filter only is extracted from the experiments by applying inverse matrices of the conical sections. In the analytical approaches, the one-dimensional acoustic model for the leakage between the filter and the housing is developed. The predicted transmission loss shows a good agreement with the experimental results. Compared to the baseline, the leakage between the filter and housing increases transmission loss at a certain frequency and its harmonics. In addition, the transmission loss for the system with a partially blocked filter is measured. The blockage of the filter also increases the transmission loss at higher frequencies. For the simplicity of experiments to identify the leakage and blockage, the reflection coefficients at the inlet of the filter system have been measured using two different downstream conditions: open pipe and highly absorptive terminations. The experiments show that with highly absorptive terminations, it is easier to see the difference between the baseline and the defects.

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