Artigos de revistas: "Acoustical vortices"

1

Baudoin, M., e J. L. Thomas. "Acoustic Tweezers for Particle and Fluid Micromanipulation". Annual Review of Fluid Mechanics 52, n.º 1 (5 de janeiro de 2020): 205–34. http://dx.doi.org/10.1146/annurev-fluid-010719-060154.

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Acoustic tweezers powerfully enable the contactless collective or selective manipulation of microscopic objects. Trapping is achieved without pretagging, with forces several orders of magnitude larger than optical tweezers at the same input power, limiting spurious heating and enabling damage-free displacement and orientation of biological samples. In addition, the availability of acoustical coherent sources from kilo- to gigahertz frequencies enables the manipulation of a wide spectrum of particle sizes. After an introduction of the key physical concepts behind fluid and particle manipulation with acoustic radiation pressure and acoustic streaming, we highlight the emergence of specific wave fields, called acoustical vortices, as a means to manipulate particles selectively and in three dimensions with one-sided tweezers. These acoustic vortices can also be used to generate hydrodynamic vortices whose topology is controlled by the topology of the wave. We conclude with an outlook on the field's future directions.

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2

Gao, Lu, Haixiang Zheng, Qingyu Ma, Juan Tu e Dong Zhang. "Linear phase distribution of acoustical vortices". Journal of Applied Physics 116, n.º 2 (14 de julho de 2014): 024905. http://dx.doi.org/10.1063/1.4889860.

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3

Baudoin, Michael, Jean-Claude Gerbedoen, Antoine Riaud, Olivier Bou Matar, Nikolay Smagin e Jean-Louis Thomas. "Folding a focalized acoustical vortex on a flat holographic transducer: Miniaturized selective acoustical tweezers". Science Advances 5, n.º 4 (abril de 2019): eaav1967. http://dx.doi.org/10.1126/sciadv.aav1967.

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Acoustical tweezers based on focalized acoustical vortices hold the promise of precise contactless manipulation of millimeter down to submicrometer particles, microorganisms, and cells with unprecedented combined selectivity and trapping force. Yet, the widespread dissemination of this technology has been hindered by severe limitations of current systems in terms of performance and/or miniaturization and integrability. Here, we unleash the potential of focalized acoustical vortices by developing the first flat, compact, paired single electrode focalized acoustical tweezers. These tweezers rely on spiraling transducers obtained by folding a spherical acoustical vortex on a flat piezoelectric substrate. We demonstrate the ability of these tweezers to grab and displace micrometric objects in a standard microfluidic environment with unique selectivity. The simplicity of this system and its scalability to higher frequencies open tremendous perspectives in microbiology, microrobotics, and microscopy.

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4

Tay, Daniel, e Ning Xiang. "Experimental study of instantaneous sound intensities in rectangular enclosures". Journal of the Acoustical Society of America 153, n.º 3_supplement (1 de março de 2023): A23. http://dx.doi.org/10.1121/10.0018019.

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Instantaneous and time-averaged intensities are relevant field quantities in architectural acoustics investigations. Modeling of intensity flows in coupled volumes and the effect of absorptive material on its trajectory in reverberation chambers have been studied recently. This work focuses on vortical energy flows with a derivation of instantaneous intensity in enclosed spaces and an experimental effort for investigating the changes over time in all field quantities of interest—instantaneous intensity, pressure, and velocity simultaneously. In this study, the scale modeling technique is applied to investigate instantaneous intensity flows experimentally measured using pressure-3D velocity sensors in a rectangular room. Experimental results suggest the presence of vortical intensity modes at specific frequencies correlated to the room dimensions. The resulting simulation of intensity vortices has potential applications in the acoustical design and analysis of complex room geometries where sound energy flows play a major role in the acoustics of the space such as that of coupled-volume spaces and small rooms for critical listening.

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5

Yang, Ling, Qingyu Ma, Juan Tu e Dong Zhang. "Phase-coded approach for controllable generation of acoustical vortices". Journal of Applied Physics 113, n.º 15 (21 de abril de 2013): 154904. http://dx.doi.org/10.1063/1.4801894.

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6

Zheng, Haixiang, Lu Gao, Qingyu Ma, Yafei Dai e Dong Zhang. "Pressure distribution based optimization of phase-coded acoustical vortices". Journal of Applied Physics 115, n.º 8 (28 de fevereiro de 2014): 084909. http://dx.doi.org/10.1063/1.4867046.

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7

Gong, Zhixiong, e Michael Baudoin. "Three-dimensional trapping and assembly with synchronized spherical acoustical vortices". Journal of the Acoustical Society of America 148, n.º 4 (outubro de 2020): 2784. http://dx.doi.org/10.1121/1.5147746.

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8

Brunet, Thomas, Jean-Louis Thomas, Régis Marchiano e François Coulouvrat. "Experimental investigation of 3D shock waves on nonlinear acoustical vortices". Physics Procedia 3, n.º 1 (janeiro de 2010): 905–11. http://dx.doi.org/10.1016/j.phpro.2010.01.116.

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Brunet, Thomas, Jean-Louis Thomas, Régis Marchiano e François Coulouvrat. "Experimental observation of azimuthal shock waves on nonlinear acoustical vortices". New Journal of Physics 11, n.º 1 (7 de janeiro de 2009): 013002. http://dx.doi.org/10.1088/1367-2630/11/1/013002.

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Volke-Sepúlveda, K., A. O. Santillán e R. R. Boullosa. "Transfer of Angular Momentum to Matter from Acoustical Vortices in Free Space". Topologica 2, n.º 1 (2009): 016. http://dx.doi.org/10.3731/topologica.2.016.

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11

Baudoin, Michael, Jean-Claude Gerbedoen, Antoine Riaud, Olivier Bou Matar, Nikolay Smagin e Jean-Louis Thomas. "Compact selective tweezers based on focalized acoustical vortices and spiraling interdigitated transducers". Journal of the Acoustical Society of America 144, n.º 3 (setembro de 2018): 1896. http://dx.doi.org/10.1121/1.5068310.

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12

Riaud, Antoine, Michael Baudoin, Jean-Louis Thomas e Olivier Bou Matar. "On-chip generation of acoustical vortices with swirling surface acoustic waves for single particle manipulation and vorticity control". Journal of the Acoustical Society of America 139, n.º 4 (abril de 2016): 2072. http://dx.doi.org/10.1121/1.4950145.

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13

Bode, Florin, Claudiu Patrascu e Ilinca Nastase. "Heat and mass transfer enhancement strategies by impinging jets: A literature review". Thermal Science, n.º 00 (2020): 227. http://dx.doi.org/10.2298/tsci200713227b.

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Heat and mass transfer can be greatly increased when using impinging jets, regardless the application. The reason behind this is the complex behavior of the impinging jet flow which is leading to the generation of a multitude of flow phenomena, like: large-scale structures, small scale turbulent mixing, large curvature involving strong normal stresses and strong shear, stagnation, separation and re-attachment of the wall boundary layers, increased heat transfer at the impinged plate. All these phenomena listed above have highly unsteady nature and even though a lot of scientific studies have approached this subject, the impinging jet is not fully understood due to the difficulties of carrying out detailed experimental and numerically investigations. Nevertheless, for heat transfer enhancement in impinging jet applications, both passive and active strategies are employed. The effect of nozzle geometry and the impinging surface macrostructure modification are some of the most prominent passive strategies. On the other side, the most used active strategies utilize acoustical and mechanical oscillations in the exit plane of the flow, which in certain situations favors mixing enhancement. This is favored by the intensification of some instabilities and by the onset of large scale vortices with important levels of energy.

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14

Day, Joseph, e J. M. Quinlan. "Modeling nonlinear acoustic damping due to flow separation". Journal of the Acoustical Society of America 151, n.º 4 (abril de 2022): A272. http://dx.doi.org/10.1121/10.0011307.

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Nonlinear acoustic damping has been observed in many high-amplitude acoustic systems as a result of flow separation and shear layer vortical motion, eventually transforming some of the acoustical energy into heat. The amount of nonlinear acoustic damping helps to determine the nonlinear limit cycle amplitude, e.g., damping caused by baffle blades in a liquid rocket engine to reduce combustion instabilities. The damping mechanism is dependent on both the location and phase of flow separation. Identifying the flow separation is a function of both the boundary layer growth and the acoustically imposed pressure gradient. When the acoustic pressure gradient is adverse, the boundary layer is more prone to separation. Using this as a basis, a model can be created that is applicable to general geometry, which will then be used to approximate the nonlinear acoustic damping in various situations. The constructed model will be compared to established cases, such as an orifice in a duct, to validate the model.

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15

Day, Joseph, e J. M. Quinlan. "Modeling nonlinear acoustic damping due to flow separation". Journal of the Acoustical Society of America 152, n.º 4 (outubro de 2022): A52. http://dx.doi.org/10.1121/10.0015512.

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Nonlinear acoustic damping has been observed in many high-amplitude acoustic systems as a result of flow separation and shear layer vortical motion, eventually transforming some of the acoustical energy into heat. The amount of nonlinear acoustic damping helps determine the nonlinear limit cycle amplitude, e.g., damping caused by baffle blades in a liquid rocket engine to reduce combustion instabilities. The damping mechanism is dependent on both the location and phase of flow separation. Identifying the flow separation is a function of both the boundary layer growth and the acoustically imposed pressure gradient. When the acoustic pressure gradient is adverse, the boundary layer is more prone to separation. Using this as a basis, a model can be created that is applicable to general geometry, which will then be used to approximate the nonlinear acoustic damping in various situations. The constructed model will be compared to established cases, such as an orifice in a duct, to validate the model.

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16

FUKUMA, Akitomo, Hiroshi YOKOYAMA, Manato KAWAI, Kenji KAWASAKI, Ichiro YAMAGIWA, Masahito NISHIKAWARA e Hideki YANADA. "Direct aeroacoustic simulation of a flow through an expanding pipe with orifice plates". INTER-NOISE and NOISE-CON Congress and Conference Proceedings 268, n.º 8 (30 de novembro de 2023): 663–72. http://dx.doi.org/10.3397/in_2023_0109.

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Expanding pipes with orifice plates are utilized as silencers for fluid machinery. However, tonal sounds can be generated from flows through the silencers with such a configuration. To clarify the mechanism of tonal sound generation from a flow over a circular expanding pipe with orifice plates, flow and acoustic fields were directly solved on the basis of the compressible Navier-Stokes equations. Prediction results demonstrated that tonal sounds occurred at multiple frequencies. The phase-averaged flow fields for each frequency indicated that vortex rings or spiral vortices were periodically shed in the flow around the orifice plates. Acoustic radiation occurred owing to the collision of these vortices with the orifice plates, which led to the occurrence of acoustic resonance in the expanding pipe. The predicted circumferential phase distributions of pressure fluctuations demonstrated the coexistence of different acoustic modes in the expanding pipe. The relationship between acoustic modes and vortical behaviors was presented. The effects of inflow Mach number on the vortex structures and acoustic modes for the resonance were also discussed.

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17

Zhu, Haodong, Peiran Zhang, Zhanwei Zhong, Jianping Xia, Joseph Rich, John Mai, Xingyu Su et al. "Acoustohydrodynamic tweezers via spatial arrangement of streaming vortices". Science Advances 7, n.º 2 (janeiro de 2021): eabc7885. http://dx.doi.org/10.1126/sciadv.abc7885.

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Acoustics-based tweezers provide a unique toolset for contactless, label-free, and precise manipulation of bioparticles and bioanalytes. Most acoustic tweezers rely on acoustic radiation forces; however, the accompanying acoustic streaming often generates unpredictable effects due to its nonlinear nature and high sensitivity to the three-dimensional boundary conditions. Here, we demonstrate acoustohydrodynamic tweezers, which generate stable, symmetric pairs of vortices to create hydrodynamic traps for object manipulation. These stable vortices enable predictable control of a flow field, which translates into controlled motion of droplets or particles on the operating surface. We built a programmable droplet-handling platform to demonstrate the basic functions of planar-omnidirectional droplet transport, merging droplets, and in situ mixing via a sequential cascade of biochemical reactions. Our acoustohydrodynamic tweezers enables improved control of acoustic streaming and demonstrates a previously unidentified method for contact-free manipulation of bioanalytes and digitalized liquid handling based on a compact and scalable functional unit.

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18

Powell, Alan. "Why Do Vortices Generate Sound?" Journal of Mechanical Design 117, B (1 de junho de 1995): 252–60. http://dx.doi.org/10.1115/1.2836464.

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Emphasizing physical pictures with a minimum of analysis, an introductory account is presented as to how vortices generate sound. Based on the observation that a vortex ring induces the same hydrodynamic (incompressible) flow as does a dipole sheet of the same shape, simple physical arguments for sound generation by vorticity are presented, first in terms of moving vortex rings of fixed strength and then of fixed rings of variable strength. These lead to the formal results of the theory of vortex sound, with the source expressed in terms of the vortex force ρ(u∧ ζ) and of the form introduced by Mo¨hring in terms of the vortex moment (y∧ ζ′), (ρ is the constant fluid density, u the flow velocity, ζ = ∇ ∧u the vorticity and y is the flow coordinate). The simple “Contiguous Method” of finding the contiguous acoustic field surrounding an acoustically compact hydrodynamic (incompressible) field is also discussed. Some very simple vortex flows illustrate the various ideas. These are all for acoustically compact, low Mach number flows of an inviscid fluid, except that a simple argument for the effect of viscous dissipation is given and its relevance to the “dilatation” of a vortex is mentioned.

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19

Powell, Alan. "Why Do Vortices Generate Sound?" Journal of Vibration and Acoustics 117, B (1 de junho de 1995): 252–60. http://dx.doi.org/10.1115/1.2838670.

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Emphasizing physical pictures with a minimum of analysis, an introductory account is presented as to how vortices generate sound. Based on the observation that a vortex ring induces the same hydrodynamic (incompressible) flow as does a dipole sheet of the same shape, simple physical arguments for sound generation by vorticity are presented, first in terms of moving vortex rings of fixed strength and then of fixed rings of variable strength. These lead to the formal results of the theory of vortex sound, with the source expressed in terms of the vortex force ρ(u∧ ζ) and of the form introduced by Mo¨hring in terms of the vortex moment (y∧ ζ′), (ρ is the constant fluid density, u the flow velocity, ζ = ∇ ∧u the vorticity and y is the flow coordinate). The simple “Contiguous Method” of finding the contiguous acoustic field surrounding an acoustically compact hydrodynamic (incompressible) field is also discussed. Some very simple vortex flows illustrate the various ideas. These are all for acoustically compact, low Mach number flows of an inviscid fluid, except that a simple argument for the effect of viscous dissipation is given and its relevance to the “dilatation” of a vortex is mentioned.

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20

Day, Joseph, e J. M. Quinlan. "Modeling nonlinear acoustic damping due to flow separation over a baffle blade". Journal of the Acoustical Society of America 153, n.º 3_supplement (1 de março de 2023): A240. http://dx.doi.org/10.1121/10.0018768.

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Nonlinear acoustic damping has been observed in many high-amplitude acoustic systems as a result of flow separation and shear layer vortical motion, eventually transforming some of the acoustical energy into heat. The amount of nonlinear acoustic damping helps determine the nonlinear limit cycle amplitude, e.g., damping caused by baffle blades in a liquid rocket engine to reduce combustion instabilities. The damping mechanism is dependent on both the location and phase of flow separation. Flow separation is a function of both the boundary layer growth and the acoustically imposed pressure gradient. When the acoustic pressure gradient is adverse, the boundary layer is more prone to separation. Using this as a basis, a model can be created, applicable to general geometry, which can approximate nonlinear acoustic damping in flow over baffle blades. The constructed model will be compared to established cases, such as an orifice in a duct, to validate the model. Once validated, this model can approximate the nonlinear acoustic damping caused by a baffle blade, for both standing and traveling waves, and will be compared to experimental results to test accuracy. This model could result in designing rocket engines based on engine specific damping requirements rather than past successful designs.

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21

Leboeuf, Richard L., e Rabindra D. Mehta. "Measurements of spanwise scale change in a forced mixing layer". Journal of Fluid Mechanics 293 (25 de junho de 1995): 305–19. http://dx.doi.org/10.1017/s0022112095001728.

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Spanwise scale changes of the streamwise vortical structure in a plane forced mixing layer have been investigated through direct measurements. Detailed three-dimensional phase-averaged measurements were obtained of the spanwise and streamwise vorticity in a forced mixing layer undergoing three spanwise roller pairings. A two-stream mixing layer with a velocity ratio (U2/U1) of 0.6 and laminar initial boundary layers was generated in a mixing-layer wind tunnel. Acoustic forcing, consisting of a fundamental roll-up frequency and its first, second and third subharmonics, was used to phase-lock the initial development and the first three pairings of the spanwise rollers. Although the overall spanwise scale remained unchanged through the first two roller pairings, some (cyclic) ‘readjustment’ of the weaker streamwise structures was observed. The overall spanwise scale doubled during the third roller pairing. For the first time, one of the proposed mechanisms for the scale change has been identified and its details measured directly. The weakest (positive) streamwise vortex is split into two and displaced by stronger neighbouring (negative) vortices. These two vortices (of the same sign) then merge together, thus doubling the spanwise scale and circulation of the resulting streamwise vortical structure.

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22

Stenflo, L. "Acoustic solitary vortices". Physics of Fluids 30, n.º 10 (1987): 3297. http://dx.doi.org/10.1063/1.866458.

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Stenflo, L. "Acoustic gravity vortices". Physica Scripta 41, n.º 5 (1 de maio de 1990): 641–42. http://dx.doi.org/10.1088/0031-8949/41/5/001.

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Wu, Ying, e Kai–lun Yao. "Acoustic Gravity Vortices". Communications in Theoretical Physics 14, n.º 2 (setembro de 1990): 253–56. http://dx.doi.org/10.1088/0253-6102/14/2/253.

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25

Goldstein, R. J., e Boyong He. "Energy Separation and Acoustic Interaction in Flow Across a Circular Cylinder". Journal of Heat Transfer 123, n.º 4 (12 de fevereiro de 2001): 682–87. http://dx.doi.org/10.1115/1.1378020.

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Energy separation in a flow around an adiabatic circular cylinder is investigated using a surface-mounted thermocouple. Energy separation mechanisms in different regions around the cylinder are discussed. Velocity measurements near the rear stagnation point and acoustic measurements indicate that shedding vortices and the wind tunnel intrinsic resonant acoustics can strengthen each other when their frequencies match producing strong energy separation.

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26

Guo, Shifang, Zhen Ya, Pengying Wu e Mingxi Wan. "A review on acoustic vortices: Generation, characterization, applications and perspectives". Journal of Applied Physics 132, n.º 21 (7 de dezembro de 2022): 210701. http://dx.doi.org/10.1063/5.0107785.

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Acoustic vortices provide a single-beam approach to manipulate objects with sizes from nanometers to millimeters, gaining increasing interest in recent years. The helical beam renders them good ability to trap particles in three dimensions stably. At the same time, the orbital angular momentum of acoustic vortices can be used to realize object rotation and data transmission. In this review, we summarize the generation and characterization of acoustic vortices. Furthermore, we present the application of acoustic vortices in particle manipulation, object rotation, acoustic communication, and especially in the biomedical field. Finally, perspectives on the future directions for acoustic vortex research are discussed.

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Jovanović, D., L. Stenflo e P. K. Shukla. "Acoustic gravity tripolar vortices". Physics Letters A 279, n.º 1-2 (janeiro de 2001): 70–74. http://dx.doi.org/10.1016/s0375-9601(00)00796-9.

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28

Naugolnykh, Konstantin A. "Acoustic instability of vortices". Journal of the Acoustical Society of America 133, n.º 5 (maio de 2013): 3555. http://dx.doi.org/10.1121/1.4806464.

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Dhia, A. S. Bonnet-Ben, J. F. Mercier, F. Millot, S. Pernet e E. Peynaud. "Time-Harmonic Acoustic Scattering in a Complex Flow: A Full Coupling Between Acoustics and Hydrodynamics". Communications in Computational Physics 11, n.º 2 (fevereiro de 2012): 555–72. http://dx.doi.org/10.4208/cicp.221209.030111s.

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AbstractFor the numerical simulation of time harmonic acoustic scattering in a complex geometry, in presence of an arbitrary mean flow, the main difficulty is the coexistence and the coupling of two very different phenomena: acoustic propagation and convection of vortices. We consider a linearized formulation coupling an augmented Galbrun equation (for the perturbation of displacement) with a time harmonic convection equation (for the vortices). We first establish the well-posedness of this time harmonic convection equation in the appropriate mathematical framework. Then the complete problem, with Perfectly Matched Layers at the artificial boundaries, is proved to be coercive + compact, and a hybrid numerical method for the solution is proposed, coupling finite elements for the Galbrun equation and a Discontinuous Galerkin scheme for the convection equation. Finally a 2D numerical result shows the efficiency of the method.

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Zhong, Siyang, e Xin Zhang. "A sound extrapolation method for aeroacoustics far-field prediction in presence of vortical waves". Journal of Fluid Mechanics 820 (8 de maio de 2017): 424–50. http://dx.doi.org/10.1017/jfm.2017.219.

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Off-surface integral solutions to an inhomogeneous wave equation based on acoustic analogy could suffer from spurious wave contamination when volume integrals are ignored for computation efficiency and vortical/turbulent gusts are convected across the integration surfaces, leading to erroneous far-field directivity predictions. Vortical gusts often exist in aerodynamic flows and it is inevitable their effects are present on the integration surface. In this work, we propose a new sound extrapolation method for acoustic far-field directivity prediction in the presence of vortical gusts, which overcomes the deficiencies in the existing methods. The Euler equations are rearranged to an alternative form in terms of fluctuation variables that contains the possible acoustical and vortical waves. Then the equations are manipulated to an inhomogeneous wave equation with source terms corresponding to surface and volume integrals. With the new formulation, spurious monopole and dipole noise produced by vortical gusts can be suppressed on account of the solenoidal property of the vortical waves and a simple convection process. It is therefore valid to ignore the volume integrals and preserve the sound properties. The resulting new acoustic inhomogeneous convected wave equations could be solved by means of the Green’s function method. Validation and verification cases are investigated, and the proposed method shows a capacity of accurate sound prediction for these cases. The new method is also applied to the challenging airfoil leading edge noise problems by injecting vortical waves into the computational domain and performing aeroacoustic studies at both subsonic and transonic speeds. In the case of a transonic airfoil leading edge noise problem, shocks are present on the airfoil surface. Good agreements of the directivity patterns are obtained compared with direct computation results.

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HATTORI, Y., e STEFAN G. LLEWELLYN SMITH. "Axisymmetric acoustic scattering by vortices". Journal of Fluid Mechanics 473 (10 de dezembro de 2002): 275–94. http://dx.doi.org/10.1017/s002211200200246x.

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The scattering of acoustic waves by compact three-dimensional axisymmetric vortices is studied using direct numerical simulation in the case where the incoming wave is aligned with the symmetry axis and the direction of propagation of the vortices. The cases of scattering by Hill’s spherical vortex and Gaussian vortex rings are examined, and results are compared with predictions obtained by matched asymptotic expansions and the Born approximation. Good agreement is obtained for long waves, with the Born approximation usually giving better predictions, especially as the difference in scale between vortex and incoming waves decreases and as the Mach number of the flow increases. An improved version of the Born approximation which takes into account higher-order effects in Mach number gives the best agreement.

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Baran, Błażej, Krystian Machaj, Ziemowit Malecha e Krzysztof Tomczuk. "Numerical Study of Baroclinic Acoustic Streaming Phenomenon for Various Flow Parameters". Energies 15, n.º 3 (25 de janeiro de 2022): 854. http://dx.doi.org/10.3390/en15030854.

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The article presents a numerical study of the large-amplitude, acoustically-driven streaming flow for different frequencies of the acoustic wave and different temperature gradients between hot and cold surfaces. The geometries studied were mainly two-dimensional rectangular resonators of different lengths, but also one three-dimensional rectangular resonator and one long and narrow channel, representative of a typical U-shaped resistance thermometer. The applied numerical model was based on the Navier–Stokes compressible equations, the ideal gas model, and finite volume discretization. The oscillating wall of the considered geometries was modeled as a dynamically moving boundary of the numerical mesh. The length of the resonators was adjusted to one period of the acoustic wave. The research confirmed that baroclinic acoustic streaming flow was largely independent of frequency, and its intensity increased with the temperature gradient between the hot and cold surface. Interestingly, a slight maximum was observed for some oscillation frequencies. In the case of the long and narrow channel, acoustic streaming manifested itself as a long row of counter-rotating vortices that varied slightly along the channel. 3D calculations showed that a three-dimensional pair of streaming vortices had formed in the resonator. Examination of the flow in selected cross-sections showed that the intensity of streaming gradually decreased as it approached the side walls of the resonator creating a quasi-parabolic profile. The future development of the research will focus on fully 3D calculations and precise identification of the influence of the bounding walls on the streaming flow.

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FORD, RUPERT, e STEFAN G. LLEWELLYN SMITH. "Scattering of acoustic waves by a vortex". Journal of Fluid Mechanics 386 (10 de maio de 1999): 305–28. http://dx.doi.org/10.1017/s0022112099004371.

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We investigate the scattering of a plane acoustic wave by an axisymmetric vortex in two dimensions. We consider vortices with localized vorticity, arbitrary circulation and small Mach number. The wavelength of the acoustic waves is assumed to be much longer than the scale of the vortex. This enables us to define two asymptotic regions: an inner, vortical region, and an outer, wave region. The solution is then developed in the two regions using matched asymptotic expansions, with the Mach number as the expansion parameter. The leading-order scattered wave field consists of two components. One component arises from the interaction in the vortical region, and takes the form of a dipolar wave. The other component arises from the interaction in the wave region. For an incident wave with wavenumber k propagating in the positive X-direction, a steepest descents analysis shows that, in the far-field limit, the leading-order scattered field takes the form i(π−θ)eikX+½cosθcot(½θ) (2π/kR)1/2ei(kR−π/4), where θ is the usual polar angle. This expression is not valid in a parabolic region centred on the positive X-axis, where kRθ2=O(1). A different asymptotic solution is appropriate in this region. The two solutions match onto each other to give a leading-order scattering amplitude that is finite and single-valued everywhere, and that vanishes along the X-axis. The next term in the expansion in Mach number has a non-zero far-field response along the X-axis.

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Jackson, Beren R., e Sam M. Dakka. "Computational fluid dynamics investigation into flow behavior and acoustic mechanisms at the trailing edge of an airfoil". Noise & Vibration Worldwide 49, n.º 1 (janeiro de 2018): 20–31. http://dx.doi.org/10.1177/0957456517751455.

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Airfoil self-noise or trailing edge noise and shear noise were investigated computationally for a NACA 0012 airfoil section, focusing on noise mechanisms at the trailing edge to identify and understand sources of noise production using ANSYS Fluent. A two-dimensional computational fluid dynamics simulation has been performed for 0°, 8°, and 16° airfoil angles of attack capturing surface pressure contours, contours of turbulent intensity, contours of surface acoustic power level, vorticity magnitude levels across the airfoil profile, and x- and y-directional self-noise and shear noise sources across the airfoil profile. The results indicate that pressure gradients at the upper surface do increase as the angle of attack increases, which is a measure of vortices near the surface of the trailing edge associated with turbulence cease as the boundary layer begins to separate. Comparison of the turbulent intensity contours with surface acoustic power level contours demonstrated direct correlation between the energy contributed by turbulent structures (i.e. vortices) and the level of noise measured at the surface and within the boundary layer of the airfoil. As angle of attack is increased, both x and y sources have the same trends; however, y sources (perpendicular to the free-stream flow) appear to have a bigger impact as angle of attack is increased. Furthermore, as the angle of attack increased, shear noise contributes less and less energy further downstream of the airfoil and becomes dominated by noise energy from vortical structures within turbulence. The two-dimensional computational fluid dynamics simulation revealed that pressure, turbulent intensity, and surface acoustic power contours further corroborated the previously tested noise observations phenomena at the trailing edge of the airfoil.

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Abdikamalov, E., T. Foglizzo e O. Mukazhanov. "Impact of rotation on the evolution of convective vortices in collapsing stars". Monthly Notices of the Royal Astronomical Society 503, n.º 3 (10 de março de 2021): 3617–28. http://dx.doi.org/10.1093/mnras/stab715.

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ABSTRACT We study the impact of rotation on the hydrodynamic evolution of convective vortices during stellar collapse. Using linear hydrodynamics equations, we study the evolution of the vortices from their initial radii in convective shells down to smaller radii where they are expected to encounter the supernova shock. We find that the evolution of vortices is mainly governed by two effects: the acceleration of infall and the accompanying speed up of rotation. The former effect leads to the radial stretching of vortices, which limits the vortex velocities. The latter effect leads to the angular deformation of vortices in the direction of rotation, amplifying their non-radial velocity. We show that the radial velocities of the vortices are not significantly affected by rotation. We study acoustic wave emission and find that it is not sensitive to rotation. Finally, we analyse the impact of the corotation point and find that it has a small impact on the overall acoustic wave emission.

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Fu, Yangyang, Chen Shen, Xiaohui Zhu, Junfei Li, Youwen Liu, Steven A. Cummer e Yadong Xu. "Sound vortex diffraction via topological charge in phase gradient metagratings". Science Advances 6, n.º 40 (outubro de 2020): eaba9876. http://dx.doi.org/10.1126/sciadv.aba9876.

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Wave fields with orbital angular momentum (OAM) have been widely investigated in metasurfaces. By engineering acoustic metasurfaces with phase gradient elements, phase twisting is commonly used to obtain acoustic OAM. However, it has limited ability to manipulate sound vortices, and a more powerful mechanism for sound vortex manipulation is strongly desired. Here, we propose the diffraction mechanism to manipulate sound vortices in a cylindrical waveguide with phase gradient metagratings (PGMs). A sound vortex diffraction law is theoretically revealed based on the generalized conservation principle of topological charge. This diffraction law can explain and predict the complicated diffraction phenomena of sound vortices, as confirmed by numerical simulations. To exemplify our findings, we designed and experimentally verified a PGM based on Helmholtz resonators that support asymmetric transmission of sound vortices. Our work provides previously unidentified opportunities for manipulating sound vortices, which can advance more versatile design for OAM-based devices.

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37

Goldstein, M. E., e Pierre Ricco. "Non-localized boundary layer instabilities resulting from leading edge receptivity at moderate supersonic Mach numbers". Journal of Fluid Mechanics 838 (16 de janeiro de 2018): 435–77. http://dx.doi.org/10.1017/jfm.2017.889.

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This paper uses matched asymptotic expansions to study the non-localized (which we refer to as global) boundary layer instabilities generated by free-stream acoustic and vortical disturbances at moderate supersonic Mach numbers. The vortical disturbances produce an unsteady boundary layer flow that develops into oblique instability waves with a viscous triple-deck structure in the downstream region. The acoustic disturbances (which for reasons given herein are assumed to have obliqueness angles that are close to a certain critical angle) generate slow boundary layer disturbances which eventually develop into oblique stable disturbances with an inviscid triple-deck structure in a region that lies downstream of the viscous triple-deck region. The paper shows that both the vortically generated instabilities and the acoustically generated oblique disturbances ultimately develop into modified Rayleigh-type instabilities (which can either grow or decay) further downstream.

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Kurosaka, M., J. B. Gertz, J. E. Graham, J. R. Goodman, P. Sundaram, W. C. Riner, H. Kuroda e W. L. Hankey. "Energy separation in a vortex street". Journal of Fluid Mechanics 178 (maio de 1987): 1–29. http://dx.doi.org/10.1017/s0022112087001095.

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When a bluff body is placed in a crossflow, the total temperature in its wake can become substantially less than the incoming one, as manifested by the fact that the recovery factor R on its rearmost surface takes negative values at high subsonic flow: this is the phenomenon referred to here as the Eckert-Weise effect. Although a vortex street has been a suspected cause, the issue of whether this is so, and what the mechanism is, has remained unsettled. In this experimental and theoretical investigation, we first examine the cause of the Eckert-Weise effect by enhancing the vortex shedding through acoustic synchronization: resonance between the vortex shedding and transversely standing acoustic waves in a wind tunnel. At the lowest synchronization, where a ringing sound emanates from the wind tunnel, R at the rearmost section of the cylinder is found to become negative even at a Mach number of 0.2; the base pressure (Cpb) takes dips correspondingly, indicative of the intensification of the vortex street. At this lowest acoustic resonance, the decrease of R and Cpb, uniform along the span, agrees with the expectation based on the spanwise uniformity of the lowest standing wave. At the next acoustic resonance where the standing wave now varies along the span, the corresponding dips in R and Cpb, non-uniform along the span, reveals an interesting ‘strip-theory’-like behaviour of the vortex intensities in the vortex street. These results correlating the change in R with Cpb confirm that the Eckert-Weise effect is indeed caused by the vortex shedding, the mechanism of which is examined theoretically in the latter half of the paper.A simple theoretical argument, bolstered by a full numerical simulation, shows that the time-varying static pressure field due to the vortex movement separates the instantaneous total temperature into hot and cold spots located around vortices; once time-averaged, however, the total temperature distribution conceals the presence of hot spots and takes the guise of a colder wake, the Eckert-Weise effect. Therefore the correct explanation of the Eckert-Weise effect, a time-averaged phenomenon, emerges only out of, and only as a superposition of, instantaneous total temperature separation around vortices. Such a separation is not confined to the outside of vortex cores; every vortex in its entirety becomes thermally separated. Nor is it limited to the far downstream equilibrium configuration of the Kármán vortex street but applies to the important near-wake vortices, and to any three-dimensional vortical structure as well. For low subsonic flows in particular, this dynamical explanation also leads to a similar separation of total pressure; these features may thus be potentially exploited as a general marker to identify and quantify vortices.

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Gaye, Samba, Wagdy Mahmoud e Max Denis. "Acoustic sensing of wind generated vortices in urban environments". Journal of the Acoustical Society of America 153, n.º 3_supplement (1 de março de 2023): A45. http://dx.doi.org/10.1121/10.0018095.

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In this work, generated vortices within an urban microspaces are investigated numerically and experimentally. Of particular interest are vortices within an urban street canyon. Computational fluid dynamics simulations of wind vortices are compared to experimental observation of similar urban street geometries within the District of Columbia. Additionally, the vortex and ground interaction are investigated for acoustic propagation. Preliminary results are presented and discussed.

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40

Eftekharian, Esmaeel, Paul Croaker, Steffen Marburg, Daipei Liu e Nicole Kessissoglou. "Non-negative aeroacoustic source contributions to radiated sound power". Journal of the Acoustical Society of America 153, n.º 6 (1 de junho de 2023): 3522–31. http://dx.doi.org/10.1121/10.0019855.

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A new approach that determines the contribution of aeroacoustic sources to sound power is presented. The method combines the Lighthill source distribution with an acoustic impedance matrix constructed from radiation kernels of the free-field Green's function. To demonstrate the technique, the flow noise produced by a pair of co-rotating vortices is examined. Results are initially compared with those obtained using Möhring's analogy of two-dimensional vortex sound radiation. The contribution to sound power for each component of the Lighthill tensor is presented for a range of wave numbers and vortex separation distances. For acoustically compact cases, the aeroacoustic source contributions for the diagonal components of the Lighthill tensor show a similar trend observed in sound maps for longitudinal quadruples. In contrast to the acoustically compact cases where the central focal area is mostly unchanged with variation in Mach number, significant variation in the focal areas occurs for non-acoustically compact cases. Using the aeroacoustic source contribution technique, the nature and location of dominant flow noise sources to sound power can be identified.

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Collins, David J., Bee Luan Khoo, Zhichao Ma, Andreas Winkler, Robert Weser, Hagen Schmidt, Jongyoon Han e Ye Ai. "Selective particle and cell capture in a continuous flow using micro-vortex acoustic streaming". Lab on a Chip 17, n.º 10 (2017): 1769–77. http://dx.doi.org/10.1039/c7lc00215g.

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Mann, J. Adin, e Jiri Tichy. "Acoustic energy transfer and intensity vortices". Journal of the Acoustical Society of America 79, S1 (maio de 1986): S35. http://dx.doi.org/10.1121/1.2023184.

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Haque, Q., e H. Saleem. "Ion acoustic vortices in quantum magnetoplasmas". Physics of Plasmas 15, n.º 6 (junho de 2008): 064504. http://dx.doi.org/10.1063/1.2946434.

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Bajic, Branko. "Acoustic diagnosis of singing cavitation vortices". Journal of the Acoustical Society of America 105, n.º 2 (fevereiro de 1999): 1075. http://dx.doi.org/10.1121/1.424617.

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Haque, Q., Arshad M. Mirza e Shahida Nargis. "Electron-acoustic vortices in multicomponent magnetoplasma". Physics of Plasmas 17, n.º 5 (maio de 2010): 054505. http://dx.doi.org/10.1063/1.3425853.

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MILLS, RICHARD, JOHN SHERIDAN e KERRY HOURIGAN. "Response of base suction and vortex shedding from rectangular prisms to transverse forcing". Journal of Fluid Mechanics 461 (25 de junho de 2002): 25–49. http://dx.doi.org/10.1017/s0022112002008534.

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In previous experiments, the vortex-shedding frequency in the flow around rectangular prisms has been found to follow a stepwise variation with chord-to-thickness ratio for two different situations: the natural shedding at low Reynolds number and the excitation of a resonant transverse acoustic mode of a duct for flows at moderate Reynolds numbers. This stepwise variation disappears for natural shedding at Reynolds number higher than approximately 2000; however, it is present at the higher Reynolds numbers for the acoustically perturbed case. The present experimental study shows that if the flow is forced by small transverse oscillations, similar in form to the resonant transverse acoustic mode, the leading-edge and trailing-edge vortex shedding are locked over a wide range of forcing frequencies. However, a stepwise variation in the frequency at which peak base drag occurs is found even at these higher Reynolds numbers. The stepwise frequency variation of vortex shedding in the natural shedding case and the acoustic resonance case are then explained in terms of preference of the flow to shed trailing-edge vortices at peak base drag.

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Zhong, Siyang, e Xin Zhang. "A generalized sound extrapolation method for turbulent flows". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 474, n.º 2210 (fevereiro de 2018): 20170614. http://dx.doi.org/10.1098/rspa.2017.0614.

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Sound extrapolation methods are often used to compute acoustic far-field directivities using near-field flow data in aeroacoustics applications. The results may be erroneous if the volume integrals are neglected (to save computational cost), while non-acoustic fluctuations are collected on the integration surfaces. In this work, we develop a new sound extrapolation method based on an acoustic analogy using Taylor’s hypothesis (Taylor 1938 Proc. R. Soc. Lon. A 164 , 476–490. ( doi:10.1098/rspa.1938.0032 )). Typically, a convection operator is used to filter out the acoustically inefficient components in the turbulent flows, and an acoustics dominant indirect variable D c p ′ is solved. The sound pressure p ′ at the far field is computed from D c p ′ based on the asymptotic properties of the Green’s function. Validations results for benchmark problems with well-defined sources match well with the exact solutions. For aeroacoustics applications: the sound predictions by the aerofoil–gust interaction are close to those by an earlier method specially developed to remove the effect of vortical fluctuations (Zhong & Zhang 2017 J. Fluid Mech. 820 , 424–450. ( doi:10.1017/jfm.2017.219 )); for the case of vortex shedding noise from a cylinder, the off-body predictions by the proposed method match well with the on-body Ffowcs-Williams and Hawkings result; different integration surfaces yield close predictions (of both spectra and far-field directivities) for a co-flowing jet case using an established direct numerical simulation database. The results suggest that the method may be a potential candidate for sound projection in aeroacoustics applications.

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Litvinenko, Maria, Yuriy Litvinenko, Valentin Vikhorev e Grigory Kozlov. "Influence Of Acoustic Fluctuations On The Round Jet, Formed In Curved Channel". Siberian Journal of Physics 10, n.º 2 (1 de junho de 2015): 67–72. http://dx.doi.org/10.54362/1818-7919-2015-10-2-67-72.

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The results of experimental investigations on the effect of the transverse acoustic fluctuations for subsonic round jet formed in curved channel (d = 20; 9; 1.5 mm) are presented. Using laser – smoke visualization the jet instant picture sections were received, which showed the presence of two modes jets instabilities – Kelvin – Helmholtz vortices and Dean vortices and their interaction. The influence of the acoustic excitation frequencies on the jets are shown, in particular on a wavelength of Kelvin – Helmholtz instability. The picture of the diffusion combustion of propane jet with a nozzle diameter of d = 1,5 mm without acoustic excitation and with acoustic excitation are compared. It has been observed that the diffusion flame combustion of propane is subject to transformation by the action of the acoustic field and developing instabilities in the jet.

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Vetchanin, E. V., e A. O. Kazakov. "Bifurcations and Chaos in the Dynamics of Two Point Vortices in an Acoustic Wave". International Journal of Bifurcation and Chaos 26, n.º 04 (abril de 2016): 1650063. http://dx.doi.org/10.1142/s0218127416500632.

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In this paper, we consider a system governing the motion of two point vortices in a flow excited by an external acoustic forcing. It is known that the system of two vortices is integrable in the absence of acoustic forcing. However, the addition of the acoustic forcing makes the system much more complex, and the system becomes nonintegrable and loses the phase volume preservation property. The objective of our research is to study chaotic dynamics and typical bifurcations. Numerical analysis has shown that the reversible pitchfork bifurcation is typical. Also, we show that the existence of strange attractors is not characteristic for the system under consideration.

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Conlisk, A. T. "Computation of Far-Field Sound Generation in a Fluid-Structure Interaction Problem". Journal of Vibration and Acoustics 107, n.º 2 (1 de abril de 1985): 210–15. http://dx.doi.org/10.1115/1.3269246.

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The problem of generation of sound in moving media has become an important problem in recent years. Accordingly, in this paper we examine the inviscid flow past a bump on a plane wall in which vorticity disturbances initially placed upstream convect downstream and interact with the bump. The physical situation of interest is that of a flow in which vortices are formed far upstream and then impinge on a surface protrusion. The bump in the wall is assumed to be cylindrical in shape and mounted on a mechanical spring. It may undergo nonlinear transverse oscillations as a result of the unsteady loading caused by the vortices. The flow field and the structure are then fully coupled and solutions for the vortex paths and consequent structure position must be obtained interactively and numerically at each time step. The relevant acoustic variables such as pressure, and potential may then be obtained in the limit as the Mach number M → 0 by asymptotic methods for any number of vortices. An acoustic point dipole is generated by impingement of an isolated vortex on the structure but a much more complicated behavior of the acoustic pressure is generated for more complex vortex arrays. Results for a single vortex and two vortices are presented.

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