Characteristics of penalty mode scattering by rigid splices in lined ducts

Bi, Wenping; Pagneux, Vincent; Lafarge, Denis; Aurégan, Yves

doi:10.1121/1.2434242

Cited by 13 publications

(4 citation statements)

References 19 publications

(17 reference statements)

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“…Numerical investigations are also possible using the method developed by Watson (1981), by expanding the perturbation within the spliced section in terms of the eigenmodes of an unspliced duct, either lined or unlined; however, there is a question over the completeness of the expansion if lined duct modes are used, since the lined duct equation is not self-adjoint. A version of Watson's method, derived by Pagneux, Amir & Kergomard (1996) and termed the multimodal method, was used to investigate liner splices without flow by Bi et al (2006Bi et al ( , 2007. They found liner splices to have a negligible scattering effect for typical aeroacoustic parameters unless the output was dominated by an especially well attenuated mode, in which case they predicted liner splices could give a significant penalty, and they also found that when the phases of incident modes were incoherent the effect of the splices was reduced compared with when the phases of the incident modes were correlated.…”

Section: Introductionmentioning

confidence: 99%

Eigenmodes of lined flow ducts with rigid splices

Davis¹,

Peake²

2011

J. Fluid Mech.

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This paper presents an analytic expression for the acoustic eigenmodes of a cylindrical lined duct with rigid axially running splices in the presence of flow. The cylindrical duct is considered to be uniformly lined except for two symmetrically positioned axially running rigid liner splices. An exact analytic expression for the acoustic pressure eigenmodes is given in terms of an azimuthal Fourier sum, with the Fourier coefficients given by a recurrence relation. Since this expression is derived using a Green’s function method, the completeness of the expansion is guaranteed. A numerical procedure is described for solving this recurrence relation, which is found to converge exponentially with respect to number of Fourier terms used and is in practice quick to compute; this is then used to give several numerical examples for both uniform and sheared mean flow. An asymptotic expression is derived to directly calculate the pressure eigenmodes for thin splices. This asymptotic expression is shown to be quantitatively accurate for ducts with very thin splices of less than 1 % unlined area and qualitatively helpful for thicker splices of the order of 6 % unlined area. A thin splice is in some cases shown to increase the damping of certain acoustic modes. The influences of thin splices and thin boundary layers are compared and found to be of comparable magnitude for the parameters considered. Trapped modes at the splices are also identified and investigated.

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Section: Introductionmentioning

confidence: 99%

Eigenmodes of lined flow ducts with rigid splices

Davis¹,

Peake²

2011

J. Fluid Mech.

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“…In the present work, the incident modes are assumed to have random initial phases. In this case, W out is given as follows [21]:…”

Section: Acoustic Power Attenuation and Transmission Lossmentioning

confidence: 99%

“…Many works, based on analytical or numerical approaches, focused on the determination of the scattering matrix. Some works, e.g., [20] and [21], used analytical formulations for the computation of the scattering matrix for acoustic problems. In these works, the liner's impedance was assumed to be constant along the duct, and could arbitrarily vary along the circumference.…”

Section: Introductionmentioning

confidence: 99%

Acoustical scattering identification with local impedance through a spectral approach

Souf

Kessentini

Bareille³

et al. 2017

Comptes Rendus. Mécanique

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Acoustical scattering in waveguides is studied in this paper. The Wave Finite Element (WFE) approach is mainly used, since it allows the reduction of problems dealing with periodic waveguides. The paper deals with guided acoustical propagation, that is, propagation in a main direction is privileged. The scattering by a locally reacting lining is first studied. The liner can be characterised by its local impedance in this case. The equivalent surface impedance is therefore calculated. Then, scattering by a porous layer is considered. A full three-dimensional modelling of the lining is preferred since porous materials are bulk reacting. The scattering matrix of the lined part is computed, and acoustical scattering of high-order modes and conversion between modes are highlighted. The acoustic power attenuation is further evaluated. The response of ducts subjected to constraining boundary conditions is also calculated. Numerical results are presented and compared to those obtained with conventional approaches.

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“…It presents an intrinsic characteristic of the duct element. For this, many researchers [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] have focused their attention on the use of the scattering matrix in their studies. In these studies, this matrix has been obtained from experimental and theoretical methods.…”

Section: Introductionmentioning

confidence: 99%

Simulation of the Uncertainties propagation in the measurement of the scattering matrix of a duct containing porous material

Hannachi,

Trabelsi,

Taktak

et al. 2023

Preprint

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The objective of a theoretical simulation of an experiment is the identification of the experience parameters which are the most sensitive to errors to take them into account during the measurement and to reduce their corresponding errors. In this study, a simulation of the experiment procedure of measurement of the scattering matrix and the acoustic power attenuation of a duct element containing porous material is presented. The influence of the errors of measurement parameters like the separation distance, the length of the porous material and the modulus of the incident pressure on the measured quantities (scattering matrix coefficients and the acoustic power attenuation) is evaluated using the Monte Carlo technique. This method is considered as a benchmark for examining uncertainty diffusion on theoretical methods. The results of the uncertainty simulation are used to determine the 95% confidence intervals and the maximum and minimum errors for each measured parameter. The obtained results show that errors on the estimation of the length of the porous material has a great influence on the transmission and reflection coefficients as well as the acoustic power attenuation of the studied duct. For the other parameters, their effects are negligible.

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Characteristics of penalty mode scattering by rigid splices in lined ducts

Cited by 13 publications

References 19 publications

Eigenmodes of lined flow ducts with rigid splices

Eigenmodes of lined flow ducts with rigid splices

Acoustical scattering identification with local impedance through a spectral approach

Simulation of the Uncertainties propagation in the measurement of the scattering matrix of a duct containing porous material

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