The Absorption of Sound Near Abrupt Axisymmetric Area Expansions

Dupere, Iain; Dowling, Ann P.

doi:10.1006/jsvi.2000.3224

Cited by 47 publications

(23 citation statements)

References 42 publications

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“…The flow is homentropic with constant mean density and sound speed (ρ,c), and the mean velocity much smaller than the sound speed. This equation has the acoustic source term on the right hand side where (ω ×ū c +ω × u c ) should be used in the bracket, but the second term is small and neglected [6,17,32].…”

Section: Summary Of Cg Model For Holes Opening To Confined Spacesmentioning

confidence: 99%

The acoustics of short circular holes opening to confined and unconfined spaces

Yang

Morgans

2017

Journal of Sound and Vibration

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The sound generated or absorbed by short circular holes with a mean flow passing through them is relevant in many practical applications. Analytical models for their acoustic response often ignore the fact that such holes open to a confined or finite space either side, or account for this e ect simply by adding an end mass inertial correction. The vortex-sound interaction within a short hole has been recently shown to strongly a ect the acoustic response at low frequencies [D.Yang and A.S.Morgans, J Sound Vib 384 (2016), pp.294 – 311]. The present study considers a semi-analytical model based on the Green’s function method to investigate how the expansion ratios either side of a short hole a ect the vortex-sound interaction within it. After accounting for expansions to confined spaces using a cylinder Green’s function method, the model is substantially simplified by applying a half-space Green’s function for expansions to large spaces. The e ect of both the up- and downstream expansion ratio on the acoustics of the hole is investigated. These hole models are then incorporated into a Helmholtz resonator model, allowing a systematic investigation into the e ect of neck-to-cavity expansion ratio and neck length. Both of these are found to a ect the resonator damping

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Section: Summary Of Cg Model For Holes Opening To Confined Spacesmentioning

confidence: 99%

The acoustics of short circular holes opening to confined and unconfined spaces

Yang

Morgans

2017

Journal of Sound and Vibration

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“…Equation 3assumes that the flow is homentropic with constant mean density and sound speed (ρ,c), and with mean velocity (ū) much smaller than the sound speed. Strictly, (ω × u) = ω ×ū +ω × u , but the second term on the right side is ignored as it is small in comparison with the first [8,23].…”

Section: Theoretical Modelmentioning

confidence: 99%

A semi-analytical model for the acoustic impedance of finite length circular holes with mean flow

Yang

Morgans

2016

Journal of Sound and Vibration

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“…Acoustic energy is transferred to a train of vortices generated at the orifice lips, and a net absorption of sound is observed in the conversion process [30]. The same kind of sound absorption mechanism operates in the case of confined jets generated by abrupt area changes [31]. The phase evolution of flow perturbations on the downstream side of the orifice is, however, not considered in these studies.…”

Section: Introductionmentioning

confidence: 96%

“…It is shown in these previous references that the acoustic conductivity strongly depends on the vortex convection velocity U cv . This velocity U cv is taken to be half of the mean aperture velocity u d in the freejet aperture case [29], while it is assumed that this quantity is nearly equal to the velocity in the orifice aperture U cv u d for confined constrictions [28,31]. In these last configurations, the presence of the wall may be represented by the method of images, and the vortex propagation velocity can be determined by adding image vortices with respect to the wall [32].…”

Section: Introductionmentioning

confidence: 99%

Mode Conversion in Acoustically Modulated Confined Jets

et al. 2009

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This paper is concerned with the response of confined low-Reynolds-number jets to external modulations of large amplitudes. The jet formed inside a duct by an orifice plate is submitted to flow perturbations impinging on the constriction from the upstream side. Vortices are generated in the downstream region, giving rise to conversion from acoustic oscillation to convective modes. Experiments and simulations are carried out to characterize this important mode conversion process. It is shown that the convective perturbation phase is a linear function of the distance from the orifice plate and of the operating frequency. Data can be collapsed into a single curve with some scatter providing a scaling rule for the phase. Numerical simulations are carried out and a method is developed to decompose the local velocity perturbations into acoustic and convective components. This is used to determine the amplitudes of upstream and downstream acoustic velocities and of the convective perturbations on the downstream side of the orifice. It is shown that the acoustic velocity approximated by a bulk oscillation in the orifice vicinity is reduced at the constriction and that this is simultaneously compensated by the generation of convective perturbations. The conversion efficiency of this process is characterized. Results obtained can be used to design flow control devices; they provide insight into the generation of vortices in orifice plate systems submitted to large pressure oscillations and could be useful to the analysis of vortex instabilities in segmented solid rocket engines.

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The Absorption of Sound Near Abrupt Axisymmetric Area Expansions

Cited by 47 publications

References 42 publications

The acoustics of short circular holes opening to confined and unconfined spaces

The acoustics of short circular holes opening to confined and unconfined spaces

A semi-analytical model for the acoustic impedance of finite length circular holes with mean flow

Mode Conversion in Acoustically Modulated Confined Jets

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