A criterion for an energy vortex in a sound field

Waterhouse, Richard; Crighton, D. G.; Ffowcs‐Williams, John E.

doi:10.1121/1.394537

Cited by 19 publications

(12 citation statements)

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“…What was not made clear previously was that a single standing wave mode does not exhibit this rotation of active intensity. To achieve rotational active intensity in a two-dimensional sound field it is typically necessary to have a line or point pressure minimum [56][57][58] This can result from the superposition of a travelling and standing wave (see below) or of two standing waves. This is supported with reference to our previous models [48][49][50], where we find that if the radiation boundary conditions (which allowed for the passage of energy across them, but still reflected a proportion of that energy to create combinations of standing and travelling waves), are replaced with rigid or free boundary conditions, the rotational patterns vanish.…”

Section: Analytical Modelmentioning

confidence: 99%

Transducer-Plane Streaming Patterns in Thin-Layer Acoustofluidic Devices

2017

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While classical Rayleigh streaming, whose circulations are perpendicular to the transducer radiating surfaces, is wellknown, transducer-plane streaming patterns, in which vortices circulate parallel to the surface driving the streaming, have been less widely discussed. Previously, a four-quadrant transducer-plane streaming pattern has been seen experimentally and subsequently investigated through numerical modelling. In this paper, we show that by considering higher order threedimensional cavity modes of rectangular channels in thin-layered acoustofluidic manipulation devices, a wider family of transducer-plane streaming patterns are found. As an example, we present a transducer-plane streaming pattern, which consists of eight streaming vortices with each occupying one octant of the plane parallel to the transducer radiating surfaces, which we call here eight-octant transducer-plane streaming. An idealised modal model is also presented to highlight and explore the conditions required to produce rotational patterns. It is found that both standing and travelling wave components are typically necessary for the formation of transducer-plane streaming patterns. In addition, other streaming patterns related to acoustic vortices and systems in which travelling waves dominate are explored with implications for potential applications. DOI:I. INTRODUCTION Acoustic streaming is steady fluid motion driven by the absorption of acoustic energy due to the interaction of acoustic waves with the fluid medium or its solid boundaries. Understanding the driving mechanisms of acoustic streaming patterns within acoustofluidic devices is important in order to precisely control it for the enhancement or suppression of acoustic streaming for applications such as particle/cell manipulation [1-8], heat transfer enhancement [9-12], noncontact surface cleaning [13][14][15][16][17], microfluidic mixing [18][19][20][21][22][23][24][25][26][27], and transport enhancement [28][29][30][31][32][33][34][35].In most bulk micro-acoustofluidic particle and cell manipulation systems of interest, the acoustic streaming fields are dominated by boundary-driven streaming [36], which is associated with acoustic dissipation in the viscous boundary layer [37]. Theoretical work on boundary-driven streaming was initiated by Rayleigh [38], and developed by a series of modifications for particular cases [39][40][41][42][43][44], which have paved the fundamental understanding of acoustic streaming flows.While Rayleigh streaming patterns (which have streaming vortices with components perpendicular to the driving boundaries) have been extensively studied [45][46][47][48], we have recently explored the mechanisms behind fourquadrant transducer-plane streaming [49] which generates streaming vortices in planes parallel to the driving boundary, and modal Rayleigh-like streaming [50] in which vortices have a roll size greater than the quarter wavelength of the main acoustic resonance and are driven by limiting velocities (the value of the streaming velocity just outside...

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Section: Analytical Modelmentioning

confidence: 99%

Transducer-Plane Streaming Patterns in Thin-Layer Acoustofluidic Devices

2017

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“…A theoretical description of the sound intensity and relationships between active and reactive intensities, as well as potential and kinetic energy densities have been first given by Smith et al [1]. A necessary and sufficient condition for a formation of energy vortex in two-dimensional and axisymmetric sound fields has been formulated by Waterhouse et al [2]. Distributions of acoustic intensity in the nearfield of point sources have been investigated by Krishnappa [3], Mann and Tichy [4], and Ham et al [5].…”

Section: Introductionmentioning

confidence: 99%

Numerical investigation of acoustic field in enclosures: Evaluation of active and reactive components of sound intensity

Meissner

2015

Journal of Sound and Vibration

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“…In the other case, when m → 0, Chapman's law (6) gives ͑+͒ = 0. Hence, energy streamlines are orthogonal to pressure-release boundaries.…”

Section: Refraction Law For Acoustic Energy Streamlinesmentioning

confidence: 99%

“…3), the vector nature of acoustic intensity measurements, as opposed to measurements of scalar acoustic pressure, revolutionized the practice of noise control. Modern applications of wave energy streamlines include studies of wave front dislocations, 8,9 source localization, 7,10 energy vortices in compressible fluids 3,6 and elastic waveguides, 11,12 nanoscale thermal radiation, 13,14 photon tunneling, 13 and bounded beam diffraction, including the Goos-Hänchen shift. 13 Examples of energy streamlines for various wave fields can be found in Refs.…”

Section: Introductionmentioning

confidence: 99%

Wave refraction at an interface: Snell’s law versus Chapman’s law

Godin

2009

The Journal of the Acoustical Society of America

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Energy streamlines provide insights into mechanisms of wave propagation and scattering and are often utilized to visualize wave fields. In contrast to rays, which are essentially an asymptotic, short-wave concept, energy streamlines adequately represent arbitrary wave fields. However, the usefulness of energy streamlines in studies of wave fields is limited by the fact that, unlike rays, no general laws governing energy streamline refraction are known. Here, a simple refraction law is derived for energy streamlines of acoustic and linearly polarized electromagnetic waves. It is shown that analysis of energy streamlines provides a helpful supplementary perspective on wave transmission through interfaces.

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A criterion for an energy vortex in a sound field

Cited by 19 publications

References 0 publications

Transducer-Plane Streaming Patterns in Thin-Layer Acoustofluidic Devices

Transducer-Plane Streaming Patterns in Thin-Layer Acoustofluidic Devices

Numerical investigation of acoustic field in enclosures: Evaluation of active and reactive components of sound intensity

Wave refraction at an interface: Snell’s law versus Chapman’s law

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