A three dimensional investigation into the acoustic performance of dissipative splitter silencers

Kirby, Ray; Williams, Paul T.; Hill, James

doi:10.1121/1.4869089

Cited by 12 publications

(16 citation statements)

References 17 publications

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“…This is important in delivering fast and effective commercial design facilities for applications where mean flow velocities may be significant, such as gas turbine exhaust systems. It also delivers a method viable for studying the effects of flow on more complex silencer designs that require a three dimensional approach, see for example the designs studied by Kirby et al [32].…”

Section: Discussionmentioning

confidence: 99%

“…Accordingly, the purpose of this article is to present and validate a theoretical methodology for use in bespoke design applications and here it is shown that one may use the point collocation method to do this. This simplified approach has significant advantages for larger and more complex silencers such as the three dimensional silencers studied by Kirby et al [32].…”

Section: Lowering Computational Demandsmentioning

confidence: 99%

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On the acoustic performance of rectangular splitter silencers in the presence of mean flow

Kirby

Amott²,

Williams

et al. 2014

Journal of Sound and Vibration

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Dissipative splitter silencers are often used to reduce the noise emitted in ventilation and gas turbine systems. It is well known that the acoustic performance of a splitter silencer changes under the influence of the convective effects of a mean gas flow and so in this article a theoretical model is developed to include the effects of mean flow. The theoretical model is based on a hybrid finite element method which enables the inclusion of bull nose fairings and a perforated screen separating the mean gas flow from a bulk reacting porous material. Predictions are compared against experimental measurements obtained both with and without mean flow. Good agreement between prediction and measurement is generally observed in the absence of mean flow, although it is seen that for silencers with a low percentage open area the silencer insertion loss is over predicted at higher frequencies. When mean flow is present, problems with the experimental methodology are observed at relatively modest mean flow velocities, and so comparison between prediction and experiment is limited to relatively low face velocities. However, experiment and theory both show that the insertion loss reduces at low frequencies when mean flow is in the direction of sound propagation, and at high frequencies the influence of mean flow is generally much smaller. Following additional theoretical investigations it is concluded that the influence of mean flow on splitter silencer performance should be accounted for at low frequencies when silencer airway velocities are greater than about 20 m/s; however, at higher frequencies one may generally neglect the effect of mean flow, even at higher velocities. Predictions obtained using the hybrid method are also compared to a simplified point collocation approach and it is demonstrated that the computationally efficient point collocation method may be used to investigate the effects of mean flow in a splitter silencer without loss of accuracy.

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Section: Discussionmentioning

confidence: 99%

Section: Lowering Computational Demandsmentioning

confidence: 99%

On the acoustic performance of rectangular splitter silencers in the presence of mean flow

Kirby

Amott²,

Williams

et al. 2014

Journal of Sound and Vibration

Self Cite

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“…The characteristic impedances of the two guides, z i /h i (see Equations. (19,20), are found to be either infinite ou zero. It is interesting to interpret these results.…”

Section: Lossless Lattices; Cut-off Frequenciesmentioning

confidence: 97%

“…Related problems are tubes with branched resonators, which can be uncoupled [10,11] or coupled [12], or with honeycomb cavities [13,14]. Other kind of systems are splitter silencers with perforated facing [15][16][17][18][19][20]. This generic problem is that of a periodic lattice of two waveguides coupled by perforations.…”

Section: Introductionmentioning

confidence: 99%

Propagation of Acoustic Waves in Two Waveguides Coupled by Perforations. II. Analysis of Periodic Lattices of Finite Length

Pachebat¹,

Kergomard²

2016

Acta Acustica united with Acustica

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The paper deals with the generic problem of two waveguides coupled by perforations, which can be perforated tube mufflers without or with partitions, possibly with absorbing materials. Other examples are ducts with branched resonators of honeycomb cavities, which can be coupled or not, and splitter silencers. Assuming low frequencies, only one mode is considered in each guide. The propagation in the two waveguides can be very different, thanks e.g. to the presence of constrictions. The model is a discrete, periodic one, based upon 4th-order impedance matrices and their diagonalization. All the calculation is analytical, thanks to the partition of the matrices in 2nd-order matrices, and allows the treatment of a very wide types of problems. Several aspects are investigated: the local or non-local character of the reaction of one guide to the other; the definition of a coupling coefficient; the effect of finite size when a lattice with n cells in inserted into an infinite guide; the relationship between the Insertion Loss and the dispersion. The assumptions are as follows: linear acoustics, no mean flow, rigid wall. However the effect of the series impedance of the perforations, which is generally ignored, is taken into account, and is discussed. When there are no losses, it is shown that, for symmetry reasons, the cutoff frequencies depend on either the series impedance or the shunt admittance, and are the eigenfrequencies of the cells of the lattice, with zero-pressure or zero-velocity at the ends of the cells.

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“…This type of silencer has also been analysed using a boundary element approach, see for example Zhou et al [9] and Wang and Wu [10]. It is common also to use the more complex bar type silencer for larger applications, and these were analysed by Kirby et al [11], and recently by Yang et al [12]. The analysis of silencer performance reported in these articles clearly demonstrate that dissipative silencers can be very effective over the medium to high frequency range; however, even the more complex designs find it difficult to deliver acceptable levels of attenuation at low frequency.…”

Section: Introductionmentioning

confidence: 99%

Reducing low frequency tonal noise in large ducts using a hybrid reactive-dissipative silencer

Williams¹,

Kirby

Hill³

et al. 2018

Applied Acoustics

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Noise generated by fans or turbines normally consists of a combination of narrow and broadband noise. To lower transmitted noise levels, it is attractive to use a combination of reactive and dissipative elements. However, this approach presents a number of challenges for larger systems. This is because reactive elements are normally only effective up to the frequency at which the first higher order modes cuts on in the duct. For larger systems, this means that reactive elements work only in the low, and often very low, frequency range, whereas dissipative elements generally work well in the medium to high frequency range. This can cause noise problems in the low to medium frequency range in larger systems. This article presents an alternative approach for delivering noise attenuation over the low to medium frequency range that is suitable for application in larger duct systems. This approach takes advantage of those splitter silencer designs commonly used in larger systems to integrate a reactive element into the splitter design. This delivers a hybrid splitter that uses a combination of dissipative and reactive elements so that the reactive element partitions the main airway. This has the advantage of introducing a quasi-planar transverse sound pressure field for each resonator in the low to medium frequency range, including frequencies above the first cut-on. It is demonstrated using predictions and measurements taken for a number of example silencers, that this approach enables reactive elements to work over an extended low to medium frequency range, including at frequencies above the first cut-on mode in the main duct. Accordingly, it is shown that a hybrid dissipative-reactive splitter design is capable of delivering improved levels of attenuation in the crucial low to medium frequency range.

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A three dimensional investigation into the acoustic performance of dissipative splitter silencers

Cited by 12 publications

References 17 publications

On the acoustic performance of rectangular splitter silencers in the presence of mean flow

On the acoustic performance of rectangular splitter silencers in the presence of mean flow

Propagation of Acoustic Waves in Two Waveguides Coupled by Perforations. II. Analysis of Periodic Lattices of Finite Length

Reducing low frequency tonal noise in large ducts using a hybrid reactive-dissipative silencer

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