Finite difference computation of acoustic scattering by small surface inhomogeneities and discontinuities

Tam, Christopher K. W.; Huang, Ju

doi:10.1016/j.jcp.2009.05.005

Cited by 5 publications

(3 citation statements)

References 32 publications

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“…A variant of this method was given by Alonso & Burdisso (2007), who considered pistons placed along the splice (with two pistons per wavelength) driven so as to approximately satisfy the rigid wall boundary condition on the splice. An approximation for resolving thin splices in time-domain simulations without overly refining the computational mesh, effectively a sub-grid-scale model, was proposed by Tam & Ju (2009).…”

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 particular, it appears that such instabilities may originate from various causes, whether phenomenological (e.g. shear-layer instabilities 21,68,69 and rupture of impedance 61,63,66,75 ) or methodological (e.g. the TDIBC model itself 49,50,61,66 and/or its algorithmic implementation, 66 the impedance eduction and/or subsequent TDIBC calibration, 76 the CAA method and/or computational set-up 50,66,68 ).…”

Section: Introductionmentioning

confidence: 99%

Further assessment of a time domain impedance boundary condition for the numerical simulation of noise-absorbing materials

Redonnet

2021

International Journal of Aeroacoustics

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In regard to the mitigation of environmental noise across major industry sectors, the present study focuses on the numerical prediction of passive noise reduction devices. Here, it is further explored how the noise attenuation induced by locally reacting noise absorbing materials (also called acoustic liners) can be simulated using a time domain highly accurate Computational AeroAcoustics (CAA) method. To this end, it is assessed how a classical Time Domain Impedance Boundary Condition (TDIBC) can effectively model acoustic liners of practical interest, including when the latter are exposed to realistic conditions (grazing flow and noise excitation). The investigation consists in numerically reproducing two experimental campaigns initially performed at NASA Langley Research Center. Two different materials are considered (honeycomb superimposed with perforate or wiremesh resistive face-sheet), each being characterized by a specific noise attenuation behaviour ( e.g. dependency on the flow conditions and/or noise excitation). Each material is tested under various flow conditions ( e.g. grazing flow of Mach up to 0.5) and/or noise source excitation ( e.g. multiple tones of level up to 140 dB each). The results demonstrate the ability of the underlying CAA/TDIBC approach to simulate realistic acoustic liners in non-trivial configurations, with enough physical accuracy ( e.g. correct capture of the noise attenuation characteristics) and numerical robustness ( e.g. absence of instabilities). The study also reveals that, independent from the CAA/TDIBC approach itself, some specific pre-processing tasks (e.g. impedance eduction and subsequent TDIBC calibration) may play a bigger role than expected, in practice.

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“…The splices can make the damper face smaller relative to the wavelength and may thus cause a significant reduction in acoustic performance at some conditions. The redistribution of this energy from these rigid splices can be shown computationally to be a function of the number and widths of the splices; although, the precise mechanics are poorly understood with the three-dimensional analysis being computationally demanding [18,20,21,22,23,24].…”

Section: Introductionmentioning

confidence: 99%

Acoustic performance of a resonating perforated liner with incident axial and circumferential acoustic modes

Cassell

Carrotte

2019

Journal of Sound and Vibration

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Perforated liners are a common form of passive damping device used in engineering applications to damp acoustic pressure fluctuations. The liner has many orifices arranged over the surface with a rear cavity, where the liner can be designed to resonate akin to an array of Helmholtz resonators in parallel. However, whilst a Helmholtz resonator is insensitive to the incident mode, the large surface area and rear cavity of a perforated liner can generate internal mode shapes that affect the acoustic performance. This paper presents a quasi-one-dimensional analytical model capable of capturing the variation in acoustic performance as the internal cavity segmentation is altered with incident higher-order acoustic modes in a narrow annular duct. Thus, the model can allow the generation of circumferential mode shapes. The model shows, when the liner is highly segmented circumferentially, the liner behaviour is akin to that with an incident axial wave. The segmentation causes the internal cavity pressure to fluctuate uniformly at a similar frequency to a Helmholtz resonator with the same effective cavity dimensions. When the cavity length is significant relative to the wavelength, circumferential mode shapes are generated within the cavity and the frequency

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Finite difference computation of acoustic scattering by small surface inhomogeneities and discontinuities

Cited by 5 publications

References 32 publications

Eigenmodes of lined flow ducts with rigid splices

Eigenmodes of lined flow ducts with rigid splices

Further assessment of a time domain impedance boundary condition for the numerical simulation of noise-absorbing materials

Acoustic performance of a resonating perforated liner with incident axial and circumferential acoustic modes

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