Effect of voids on the acoustics of perforated dissipative silencers

Selamet, Ahmet; Xu, Minghui; Lee, I J.; Huff, Norman T.

doi:10.1504/ijvnv.2006.012785

Cited by 11 publications

(17 citation statements)

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“…The bulk density is usually considered constant in the bibliography [11,16,[18][19][20][21][22][23][24][25]. Heterogeneities can appear, however, due to the silencer manufacturing process, leading to spatial variations of the bulk density and material resistivity [1][2][3][4]. These are included in the current investigation by assuming that the extension of (27) produces good predictions; that is,…”

Section: Acoustic Model Of the Materials Heterogeneity Due To Densitymentioning

confidence: 99%

“…Nevertheless, this assumption is often far away from reality, where material properties can present relevant spatial variations. Therefore, it can be important to take material heterogeneities into account when modelling bulk reacting fibrous materials as these variations are expected to significantly affect the acoustic performance of the silencer [1][2][3][4]. Material heterogeneities can be caused by an uneven filling of the chamber, for example, when the fibre is rolled around the central duct or it is pushed in the chamber.…”

Section: Introductionmentioning

confidence: 99%

“…A good agreement was found between the results derived from this method and FE calculations. In a later work of the same authors [2], the acoustic effect of voids inside the silencer, modelled by means of axially staggering filled/empty segments in the outer chamber, was studied considering a similar approach as the previous reference. In this case, the method provided good correlation with both experimental measurements and FE calculations.…”

Section: Introductionmentioning

confidence: 99%

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

Sánchez-Orgaz

Denia

Martínez‐Casas

et al. 2014

Advances in Mechanical Engineering

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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.

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Section: Acoustic Model Of the Materials Heterogeneity Due To Densitymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

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

Sánchez-Orgaz

Denia

Martínez‐Casas

et al. 2014

Advances in Mechanical Engineering

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“…These spatial variations can arise, for example, from uneven filling processes [1][2][3][4], non-uniform mean flow fields [5] and thermal gradients [6,7]. In the latter case, the difficulties associated with experimental measurements at high temperatures make it necessary to find computational approaches useful to evaluate the acoustic behaviour of the silencer.…”

Section: Introductionmentioning

confidence: 99%

Finite element based acoustic analysis of dissipative silencers with high temperature and thermal-induced heterogeneity

Denia

Sánchez-Orgaz

Martínez‐Casas

et al. 2015

Finite Elements in Analysis and Design

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A mixed finite element model has been derived for the acoustic analysis of perforated dissipative silencers including several effects simultaneously: (1) High temperature and thermal gradients in the central duct and the outer absorbent material; (2) A perforated passage carrying non-uniform axial mean flow. For such a combination, the properties of sound propagation media and flow are inhomogeneous and vary with position. The material of the outer chamber can be modelled by its complex equivalent acoustic properties, which completely determine the propagation of sound waves in the air contained in the absorbent medium. Temperature gradients introduce variations in these properties that can be evaluated through a heterogeneous temperature-dependent resistivity in combination with material models obtained at room temperature. A pressure-based wave equation for stationary medium is then used with the equivalent density and speed of sound of the absorbent material varying as functions of the spatial coordinates. Regarding the central air passage, a wave equation in terms of acoustic velocity potential can be used to model the non-uniform moving medium since the presence of temperature variations introduce not only heterogeneous acoustic properties of the air but also a gradient in the mean flow velocity. The acoustic connection between the central passage and the outer chamber is given by the acoustic impedance of the perforated duct. This impedance depends on the heterogeneous properties of the absorbent material and the non-uniform mean flow, leading to a spatial variation of the acoustic coupling and also to additional convective terms in the governing equations. The results presented show the influence of temperature, thermal gradients and mean flow on the transmission loss of automotive silencers. It has been found that high temperature and thermal-induced heterogeneity can have a significant influence on the acoustic attenuation of an automotive silencer and so should be included in theoretical models. In some particular configurations it may be relatively accurate to approximate the temperature field by using a uniform profile with an average value, specially for low resistivity materials. It has been shown, however, that this is not always possible and attenuation overestimation is likely to be predicted, mainly for high radial thermal gradients and high material flow resistivities, if the temperature distribution is not taken into account.

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“…Heterogeneitic absorbent material will significantly affect the acoustic performance of a silencer [5][6][7][8]. F. D. Denia et al establish a finite element model in analyzing the acoustic performance of automotive dissipative silencers which include a perforated duct with uniform axial mean flow and an outer chamber with heterogeneitic absorbent material.…”

mentioning

confidence: 99%