On Sound Radiation from an Open-Ended Non-Uniformly Lined Cylindrical Nozzle

Campos, L. M. B. C.; Oliveira, J. M. G. S.

doi:10.3813/aaa.918759

Cited by 2 publications

(3 citation statements)

References 34 publications

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“…The implications are that these non-sinusoidal acoustic-shear waves unlike sound rays can exchange energy with the mean flow. Thus, the sound attenuation by the wall liners [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] is coupled to acoustic-shear waves in the boundary layer that are of second-order as for sound in the absence of cross-flow, that is not considered in most of the aeroacoustic literature. The inclusion of a cross-flow raises the order of the acoustic wave equation from two to three, implying the existence of a third "vortical" mode in the boundary layer in addition to the two acoustic waves.…”

Section: Discussionmentioning

confidence: 99%

“…[8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] In order to reduce noise, the nozzle walls often use liners that, if locally reacting, can be represented by an impedance distribution. [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] The bias flow out perforated liners can have a significant effect on sound in a boundary layer 42 even for small velocities. The boundary layer may be modeled as a "double deck," with a shear flow matched to a uniform stream.…”

Section: Introductionmentioning

confidence: 99%

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Sound propagation in a lined nozzle with shear and bias flows

Campos

Legendre²

2018

International Journal of Aeroacoustics

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In this study, the propagation of waves in a two-dimensional parallel-sided nozzle is considered allowing for the combination of: (a) distinct impedances of the upper and lower walls; (b) upper and lower boundary layers with different thicknesses with linear shear velocity profiles matched to a uniform core flow; and (c) a uniform cross-flow as a bias flow out of one and into the other porous acoustic liner. The model involves an "acoustic triple deck" consisting of third-order nonsinusoidal non-plane acoustic-shear waves in the upper and lower boundary layers coupled to convected plane sinusoidal acoustic waves in the uniform core flow. The acoustic modes are determined from a dispersion relation corresponding to the vanishing of an 8 Â 8 matrix determinant, and the waveforms are combinations of two acoustic and two sets of three acousticshear waves. The eigenvalues are calculated and the waveforms are plotted for a wide range of values of the four parameters of the problem, namely: (i/ii) the core and bias flow Mach numbers; (iii) the impedances at the two walls; and (iv) the thicknesses of the two boundary layers relative to each other and the core flow. It is shown that all three main physical phenomena considered in this model can have a significant effect on the wave field: (c) a bias or cross-flow even with small Mach number M 0 $0:03 À 0:06 relative to the mean flow Mach number M 1 $0:3 À 1:2 can modify the waveforms; (b) the possibly dissimilar impedances of the lined walls can absorb (or amplify) waves more or less depending on the reactance and inductance; (a) the exchange of the wave energy with the shear flow is also important, since for the same stream velocity, a thin boundary layer has higher vorticity, and lower vorticity corresponds to a thicker boundary layer. The combination of all these three effects (a-c) leads to a large set of different waveforms in the duct that are plotted for a wide range of the parameters (i-iv) of the problem.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Sound propagation in a lined nozzle with shear and bias flows

Campos

Legendre²

2018

International Journal of Aeroacoustics

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“…[1][2][3][4] Researchers, who want to reduce noise pollution, investigated the sound radiation, and some effective methods were found. [5][6][7][8][9][10] For example, the propagation of sound in cylindrical ducts or pipes which can be assumed as a model of car exhaust or aircraft engine etc. Absorbent lining is an effective method of reducing noise from pipes.…”

Section: Introductionmentioning

confidence: 99%

Radiation analysis of sound waves from semi-infinite coated pipe

Tiryakioglu

Demír

2018

International Journal of Aeroacoustics

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An analytical solution is presented for the problem of radiation of sound waves from a semiinfinite circular cylindrical coated pipe which is partially lined from inside. By stating the total field in duct region in terms of normal waveguide modes (Dini's series) and using the Fourier transform technique elsewhere, we obtain a Wiener-Hopf equation whose solution involving three sets of infinitely many unknown expansion coefficients satisfying three systems of linear algebraic equations. This system is solved numerically and the influence of some parameters (pipe radius, impedances, extension, etc.) on the radiation phenomenon is displayed graphically.

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On Sound Radiation from an Open-Ended Non-Uniformly Lined Cylindrical Nozzle

Cited by 2 publications

References 34 publications

Sound propagation in a lined nozzle with shear and bias flows

Sound propagation in a lined nozzle with shear and bias flows

Radiation analysis of sound waves from semi-infinite coated pipe

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