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Journal articles on the topic 'Acoustical vortex'
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1
Baudoin, Michael, Jean-Claude Gerbedoen, Antoine Riaud, Olivier Bou Matar, Nikolay Smagin, and Jean-Louis Thomas. "Folding a focalized acoustical vortex on a flat holographic transducer: Miniaturized selective acoustical tweezers." Science Advances 5, no. 4 (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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Chen, R. H., M. Chaos, G. F. Haddad, and Thomas E. Mills. "Effects of vortex shedding by particles in acoustical transducers." Journal of Sound and Vibration 270, no. 1-2 (2004): 473–79. http://dx.doi.org/10.1016/s0022-460x(03)00534-0.
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Бойчук, Igor Boychuk, Перелыгин, and Dmitriy Perelygin. "INTEGRATED RESEARCHES OF ACOUSTICAL EXPOSURE ON GAS-DUST FLOW IN THE VORTEX-ACOUSTIC DISPERSER." Bulletin of Belgorod State Technological University named after. V. G. Shukhov 2, no. 1 (2016): 155–61. http://dx.doi.org/10.12737/23478.
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The article deals with the movement of gas-dispersed flow in the chamber of vortex - acoustic dis-perser. The simulation of the acoustic impact on the course of the swirling flow. It is shown that the acoustic effect for a flow leads to its inhibition. At the same time for the flow in the boundary layer takes oscillatory. Modeling has allowed to establish the nature of the distribution of acoustic oscil-lations by using single and successive acoustic wave generators, enhances the effect of braking.
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Umemura, S., and C. A. Cain. "Acoustical evaluation of a prototype sector-vortex phased-array applicator." IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control 39, no. 1 (1992): 32–38. http://dx.doi.org/10.1109/58.166807.
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Hsiao, Chao-Tsung, and Georges L. Chahine. "Scaling of Tip Vortex Cavitation Inception Noise With a Bubble Dynamics Model Accounting for Nuclei Size Distribution." Journal of Fluids Engineering 127, no. 1 (2005): 55–65. http://dx.doi.org/10.1115/1.1852476.
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The acoustic pressure generated by cavitation inception in a tip vortex flow was simulated in water containing a realistic bubble nuclei size distribution using a surface-averaged pressure (SAP) spherical bubble dynamics model. The flow field was obtained by the Reynolds-averaged Navier–Stokes computations for three geometrically similar scales of a finite-span elliptic hydrofoil. An “acoustic” criterion, which defines cavitation inception as the flow condition at which the number of acoustical “peaks” above a pre-selected pressure level exceeds a reference number per unit time, was applied to the three scales. It was found that the scaling of cavitation inception depended on the reference values (pressure amplitude and number of peaks) selected. Scaling effects (i.e., deviation from the classical σi∝Re0.4) increase as the reference inception criteria become more stringent (lower threshold pressures and less number of peaks). Larger scales tend to detect more cavitation inception events per unit time than obtained by classical scaling because a relatively larger number of nuclei are excited by the tip vortex at the larger scale due to simultaneous increase of the nuclei capture area and of the size of the vortex core. The average nuclei size in the nuclei distribution was also found to have an important impact on cavitation inception number. Scaling effects (i.e., deviation from classical expressions) become more important as the average nuclei size decreases.
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Yang, Ye, Teng Ma, Sinan Li, et al. "Self-Navigated 3D Acoustic Tweezers in Complex Media Based on Time Reversal." Research 2021 (January 4, 2021): 1–13. http://dx.doi.org/10.34133/2021/9781394.
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Acoustic tweezers have great application prospects because they allow noncontact and noninvasive manipulation of microparticles in a wide range of media. However, the nontransparency and heterogeneity of media in practical applications complicate particle trapping and manipulation. In this study, we designed a 1.04 MHz 256-element 2D matrix array for 3D acoustic tweezers to guide and monitor the entire process using real-time 3D ultrasonic images, thereby enabling acoustic manipulation in nontransparent media. Furthermore, we successfully performed dynamic 3D manipulations on multiple microparticles using multifoci and vortex traps. We achieved 3D particle manipulation in heterogeneous media (through resin baffle and ex vivo macaque and human skulls) by introducing a method based on the time reversal principle to correct the phase and amplitude distortions of the acoustic waves. Our results suggest cutting-edge applications of acoustic tweezers such as acoustical drug delivery, controlled micromachine transfer, and precise treatment.
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Pazos-Ospina, Jhon F., Joao L. Ealo, and Karen Volke-Sepulveda. "Orbital motion of a particle levitated in a standing-vortex acoustical trap." Journal of the Acoustical Society of America 144, no. 3 (2018): 1933. http://dx.doi.org/10.1121/1.5068461.
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Wassaf, Hadi S., Oliver C. Ibe, and Robert P. Dougherty. "Acoustical spectral analysis of a wake vortex cross‐section using microphone‐arrays." Journal of the Acoustical Society of America 117, no. 4 (2005): 2546. http://dx.doi.org/10.1121/1.4788468.
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Mitri, F. G. "Acoustical pulling force on rigid spheroids in single Bessel vortex tractor beams." EPL (Europhysics Letters) 112, no. 3 (2015): 34002. http://dx.doi.org/10.1209/0295-5075/112/34002.
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Wu, Juan, Ziming Kou, and Jing Liu. "The Acoustical Behavior of Contra-Rotating Fan." Mathematical Problems in Engineering 2018 (2018): 1–8. http://dx.doi.org/10.1155/2018/3739067.
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The noise produced by a contra-rotating ventilator can cause injury to humans. Therefore, it is important to reduce noise caused by ventilators. In this study, the Ffowcs Williams and Hawkings (FW-H) model was used to simulate the acoustics of four different axial impeller spacing points based on the unsteady flow field through a FBD No. 8.0 contra-rotating ventilator. Experiments were conducted to verify the correctness of the numerical model. Meanwhile, the Variable Frequency Drive (VFD) drives the two motors of 55 kW to give the impellers different speeds to distinguish different conditions. The results showed that the main noise source of the ventilator was the two rotating impellers and the area between them. For the same axial space, the noise decreased with the increase of flow rate and then decreased. And the amplitude of the discrete pulse increased gradually. It can be concluded that the vortex acoustics decreased gradually with the increase of flow rate and the rotating acoustics were the major contributor. With the axial distance increasing, the noise caused by the two impellers was weak, and the frequencies of sound pressure level moved toward medium- and low-frequency bands gradually. The suitable axial space could reduce noise and improve the working environment.
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Baresch, Diego, Régis Marchiano, and Jean-Louis Thomas. "Dipolar and quadrupolar mode dissipation of spherical probes spinning in vortex beam acoustical tweezers." Journal of the Acoustical Society of America 144, no. 3 (2018): 1897. http://dx.doi.org/10.1121/1.5068312.
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Baresch, Diego, and Valeria Garbin. "Acoustic trapping of microbubbles in complex environments and controlled payload release." Proceedings of the National Academy of Sciences 117, no. 27 (2020): 15490–96. http://dx.doi.org/10.1073/pnas.2003569117.
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Contactless manipulation of microparticles using acoustic waves holds promise for applications ranging from cell sorting to three-dimensional (3D) printing and tissue engineering. However, the unique potential of acoustic trapping to be applied in biomedical settings remains largely untapped. In particular, the main advantage of acoustic trapping over optical trapping, namely the ability of sound to propagate through thick and opaque media, has not yet been exploited in full. Here we demonstrate experimentally the use of the recently developed technique of single-beam acoustical tweezers to trap microbubbles, an important class of biomedically relevant microparticles. We show that the region of vanishing pressure of a propagating vortex beam can confine a microbubble by forcing low-amplitude, nonspherical, shape oscillations, enabling its full 3D positioning. Our interpretation is validated by the absolute calibration of the acoustic trapping force and the direct spatial mapping of isolated bubble echos, for which both find excellent agreement with our theoretical model. Furthermore, we prove the stability of the trap through centimeter-thick layers of bio-mimicking, elastic materials. Finally, we demonstrate the simultaneous trapping of nanoparticle-loaded microbubbles and activation with an independent acoustic field to trigger the release of the nanoparticles. Overall, using exclusively acoustic powering to position and actuate microbubbles paves the way toward controlled delivery of drug payloads in confined, hard-to-reach locations, with potential in vivo applications.
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Papageorgakopoulos, Johnny, and Sokrates Tsangaris. "A Numerical Method for Predicting Acoustical Wave Propagation in Open Spaces." ISRN Mechanical Engineering 2011 (May 9, 2011): 1–15. http://dx.doi.org/10.5402/2011/174031.
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We present a numerical methodology for evaluating wave propagation phenomena in two dimensions in the time domain with focus on the linear acoustic second-order wave equation. An outline of the higher-order compact discretization schemes followed by the time discretization technique is first presented. The method is completed with the addition of spatial filtering based on the same compact schemes' principles. The important role of boundary conditions is subsequently addressed. Two popular ways to truncate the computational domain in the near field are presented and compared here: first the formulation of “absorbing conditions” in the form of partial differential equations especially for the origin and second the construction of an absorbing layer surrounding the domain, in which waves (after they have exited the domain) are attenuated and decayed exponentially. Subsequently, the method is assessed by recalling three benchmark problems. In the first where a Gaussian pulse is generated and propagated in a 2D rectangular domain, the accuracy and absorbability of the boundary conditions are compared. In the second, a similar situation is investigated but under curvilinear coordinates and under the presence of a solid body which scatters the pulse. Finally the sound field inducted by the flow of corotating vortex pair is calculated and compared with the corresponding analytical solution.
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Hsiao, Chao-Tsung, Georges L. Chahine, and Han-Lieh Liu. "Scaling Effect on Prediction of Cavitation Inception in a Line Vortex Flow." Journal of Fluids Engineering 125, no. 1 (2003): 53–60. http://dx.doi.org/10.1115/1.1521956.
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The current study considers the prediction of tip vortex cavitation inception at a fundamental physics based level. Starting form the observation that cavitation inception detection is based on the “monitoring” of the interaction between bubble nuclei and the flow field, the bubble dynamics is investigated in detail. A spherical model coupled with a bubble motion equation is used to study numerically the dynamics of a nucleus in an imposed flow field. The code provides bubble size and position versus time as well as the resulting pressure at any selected monitoring position. This model is used to conduct a parametric study. Bubble size and emitted sound versus time are presented for various nuclei sizes and flow field scales in the case of an ideal Rankine vortex to which a longitudinal viscous core size diffusion model is imposed. Based on the results, one can deduce cavitation inception with the help of either an “optical inception criterion” (maximum bubble size larger than a given value) or an “acoustical inception criterion” (maximum detected noise higher than a given background value). We use here such criteria and conclude that scaling effects can be inherent to the way in which these criteria are exercised if the bubble dynamics knowledge is not taken into account.
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Mitri, F. G., and Z. E. A. Fellah. "Transverse (lateral) instantaneous force of an acoustical first-order Bessel vortex beam centered on a rigid sphere." Ultrasonics 52, no. 1 (2012): 151–55. http://dx.doi.org/10.1016/j.ultras.2011.07.009.
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Mitri, F. G. "Second-harmonic pressure generation of a non-diffracting acoustical high-order Bessel vortex beam of fractional type α". Ultrasonics 51, № 4 (2011): 496–502. http://dx.doi.org/10.1016/j.ultras.2010.12.002.
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Mitri, F. G. "Arbitrary scattering of an acoustical high-order Bessel trigonometric (non-vortex) beam by a compressible soft fluid sphere." Ultrasonics 53, no. 5 (2013): 956–61. http://dx.doi.org/10.1016/j.ultras.2012.12.008.
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MELVILLE, W. KENDALL, FABRICE VERON, and CHRISTOPHER J. WHITE. "The velocity field under breaking waves: coherent structures and turbulence." Journal of Fluid Mechanics 454 (March 10, 2002): 203–33. http://dx.doi.org/10.1017/s0022112001007078.
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Digital particle image velocimetry (DPIV) measurements of the velocity field under breaking waves in the laboratory are presented. The region of turbulent fluid directly generated by breaking is too large to be imaged in one video frame and so an ensemble-averaged representation of the flow is built up from a mosaic of image frames. It is found that breaking generates at least one coherent vortex that slowly propagates downstream at a speed consistent with the velocity induced by its image in the free surface. Both the kinetic energy of the flow and the vorticity decay approximately as t−1. The Reynolds stress of the turbulence also decays as t−1 and is, within the accuracy of the measurements, everywhere negative, consistent with downward transport of streamwise momentum. Estimates of the mometum flux from waves to currents based on the measurements of the Reynolds stress are consistent with earlier estimates. The implications of the measurements for breaking in the field are discussed. Based on geometrical optics and wave action conservation, we suggest that the presence of the breaking-induced vortex provides an explanation for the suppression of short waves by breaking. Finally, in Appendices, estimates of the majority of the terms in the turbulent kinetic energy budget are presented at an early stage in the evolution of the turbulence, and comparisons with independent acoustical measurements of breaking are presented.
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Mitri, F. G. "Spin reversal and orbital torques on a viscous fluid Rayleigh sphere located arbitrarily in acoustical Bessel vortex (spiraling) beams." Ultrasonics 72 (December 2016): 57–65. http://dx.doi.org/10.1016/j.ultras.2016.07.007.
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Liu, Xin, Yongyao Luo, Alexandre Presas, Zhengwei Wang, and Lingjiu Zhou. "Cavitation Effects on the Structural Resonance of Hydraulic Turbines: Failure Analysis in a Real Francis Turbine Runner." Energies 11, no. 9 (2018): 2320. http://dx.doi.org/10.3390/en11092320.
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When discussing potential resonances in hydraulic turbine runners, cavitation effects are usually neglected. Nevertheless, recent studies have experimentally proved, that large cavitation volumes in the proximity of flexible simple structures, such as hydrofoils, greatly modify their natural frequencies. In this paper, we analyze a resonance case in a Francis runner that leads to multiple fractures on the trailing edge of the blades, after just one day of operation at deep part load. If simple acoustic Fluid-Structure-Interaction (FSI) simulations are used, where the runner’s surrounding fluid is considered as a homogenous acoustic medium (water), the risk of structural resonances seems to be limited as the predicted natural frequencies are far enough from the excited frequencies by the flow. It is shown that the only hydraulic phenomenon which could have produced such fractures in the present case is the Rotor Stator Interaction (RSI). In order to analyze possible cavitation effects on the natural frequencies of the turbine runner, CFD simulations of the deep part load conditions have been performed, which predict large inter-blade vortex cavities. These cavities have been then introduced in the acoustical FSI model showing that under such conditions, natural frequencies of the runner increase approaching to some of the RSI excited frequencies. In particular, a possible resonance of the four-nodal diameter (4ND) mode has been found which would explain the fast behavior of the crack propagation. Furthermore, the shape and the position of the real fracture found agree with the local maximum stress spots at the junction between the trailing edges and the crown.
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Jackson, T. L., Michéle G. Macaraeg, and M. Y. Hussaini. "The role of acoustics in flame/vortex interactions." Journal of Fluid Mechanics 254 (September 1993): 579–603. http://dx.doi.org/10.1017/s0022112093002265.
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The role of acoustics in flame/vortex interactions is examined via asymptotic analysis and numerical simulation. The model consists of a one-step, irreversible Arrhenius reaction between initially unmixed species occupying adjacent half-planes which are allowed to mix and react by convection and diffusion in the presence of an acoustic field or a time-varying pressure field of small amplitude. The main emphasis is on the influence of the acoustics on the ignition time and flame structure as a function of vortex Reynolds number and initial temperature differences of the reactants.
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Powell, Alan. "Why Do Vortices Generate Sound?" Journal of Mechanical Design 117, B (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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Powell, Alan. "Why Do Vortices Generate Sound?" Journal of Vibration and Acoustics 117, B (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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Lu, Zhengli, Weichen Pan, and Yiheng Guan. "Numerical studies of transmission loss performances of asymmetric Helmholtz resonators in the presence of a grazing flow." Journal of Low Frequency Noise, Vibration and Active Control 38, no. 2 (2018): 244–54. http://dx.doi.org/10.1177/1461348418817914.
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As a typical noise-attenuating device, Helmholtz resonators are widely implemented in aero-engines and gas turbines to decrease the transmission of acoustic noise. However, an asymmetric Helmholtz resonator could be designed and implemented due to the limited space available in the engines. To examine and optimize the noise-attenuating performances of the asymmetric resonator, comparison studies are performed. For this, a two-dimensional frequency-domain model of a cylindrical duct with a grazing flow is developed. An asymmetric Helmholtz resonator is attached as a side branch. The model containing the linearized Navier–Stokes equations is validated first by comparing the predicted results with the experimental ones available in the literature. Further validation is conducted by comparing the results of an asymmetric resonator with the analytical ones available in the literature. The effects of (1) neck offset distance from the center of the resonator cavity denoted by [Formula: see text] and (2) the grazing flow Mach number [Formula: see text] are evaluated. It is shown that as the grazing flow Mach number is increased, the resonant frequencies and the maximum transmission losses are dramatically varied for a given [Formula: see text]. As [Formula: see text] is increased from 0 to 0.5 and [Formula: see text], the resonant frequencies and the maximum transmission losses are increased. However, when [Formula: see text] is lower than 0.07, i.e. [Formula: see text], the transmission loss performances are almost unchanged with [Formula: see text] increased. The optimum design of the asymmetric resonator is shown to give rise to the resonant frequency being shifted by 10% and 2–5 dB more transmission loss at higher Mach number. Finally, visualization of vortex shedding formed at the neck of the asymmetric resonator confirms that acoustical energy is transformed into kinetic energy and absorbed by the surrounding air. This study opens up a numerical design approach to optimize an asymmetric resonator.
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MILLS, RICHARD, JOHN SHERIDAN, and KERRY HOURIGAN. "Response of base suction and vortex shedding from rectangular prisms to transverse forcing." Journal of Fluid Mechanics 461 (June 25, 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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Jaworski, J. W. "Sound from aeroelastic vortex–fibre interactions." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 377, no. 2159 (2019): 20190071. http://dx.doi.org/10.1098/rsta.2019.0071.
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The motion of a line vortex moving past a one-dimensional flexible fibre is examined theoretically. A Schwarz–Christoffel conformal mapping enables the analytical solution of the potential flow field and its hydrodynamic moment on the flexible fibre, which is composed of a rigid segment constrained to angular motions on a wedge. The hydroelastic coupling of the vortex path and fibre motion affects the noise signature, which is evaluated for the special case of acoustically compact fibres embedded in a half plane. Results from this analysis attempt to address how the coupled interactions between vortical sources and flexible barbules on the upper surface of owl wings may contribute to their acoustic stealth. The analytical formulation is also amenable to application to vortex sound prediction from flexible trailing edges provided that an appropriate acoustic Green's function can be determined. This article is part of the theme issue ‘Frontiers of aeroacoustics research: theory, computation and experiment’.
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MANNEVILLE, SÉBASTIEN, CLAIRE PRADA, MICKAËL TANTER, MATHIAS FINK, and JEAN-FRANÇOIS PINTON. "ULTRASOUND PROPAGATION THROUGH A ROTATIONAL FLOW: NUMERICAL METHODS COMPARED TO EXPERIMENTS." Journal of Computational Acoustics 09, no. 03 (2001): 841–52. http://dx.doi.org/10.1142/s0218396x01001054.
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Sound propagation through a vortex is studied numerically using two different techniques: ray-tracing and finite-differences. Geometrical acoustics and ray-tracing are shown to yield a good picture of the interaction between a sound wave and a vortex when the ratio of the vortex radius to the acoustic wavelength is larger than one. In particular, this technique allows to take into account finite-size effects such as edge waves and the results are compared to experimental data. The interest of the finite-difference approach is demonstrated for cases where sound scattering occurs. We show the ability of such a simulation to account for both sound scattering and finite-size effects. Those two numerical techniques are compared and their validity is investigated.
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Peters, M. C. A. M., A. Hirschberg, A. J. Reijnen, and A. P. J. Wijnands. "Damping and reflection coefficient measurements for an open pipe at low Mach and low Helmholtz numbers." Journal of Fluid Mechanics 256 (November 1993): 499–534. http://dx.doi.org/10.1017/s0022112093002861.
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The propagation of plane acoustic waves in smooth pipes and their reflection at open pipe terminations have been studied experimentally. The accuracy of the measurements is determined by comparison of experimental data with results of linear theory for the propagation of acoustic waves in a pipe with a quiescent fluid. The damping and the reflection at an unflanged pipe termination are compared.In the presence of a fully developed turbulent mean flow the measurements of the damping confirm the results of Ronneberger & Ahrens (1977). In the high-frequency limit the quasi-laminar theory of Ronneberger (1975) predicts accurately the convective effects on the damping of acoustic waves. For low frequencies a simple theory combining the rigid-plate model of Ronneberger & Ahrens (1977) with the theoretical approach of Howe (1984) yields a fair prediction of the influence of turbulence on the shear stress. The finite response time of the turbulence near the wall to the acoustic perturbations has to be taken into account in order to explain the experimental data. The model yields a quasi-stationary limit of the damping which does not take into account the fundamental difference between the viscous and thermal dissipation observed for low frequencies.Measurements of the nonlinear behaviour of the reflection properties for unflanged pipe terminations with thin and thick walls in the absence of a mean flow confirm the theory of Disselhorst & van Wijngaarden (1980), for the low-frequency limit. It appears however that a two-dimensional theory such as proposed by Disselhorst & van Wijngaarden (1980) for the high-frequency limit underestimates the acoustical energy absorption by vortex shedding by a factor 2.5.The measured influence of wall thickness on the reflection properties of an open pipe end confirms the linear theory of Ando (1969). In the presence of a mean flow the end correction δ of an unflanged pipe end varies from the value at the high-Strouhal-number limit of δ/a = 0.61, with a the pipe radius, which is close to the value in the absence of a mean flow given by Levine & Schwinger (1948) of δ/a = 0.6133, to a value of δ/a = 0.19 in the low-Strouhal-number limit which is close to the value predicted by Rienstra (1983) of δ/a = 0.26.The pressure reflection coefficient is found to agree with the theoretical predictions by Munt (1977, 1990) and Cargill (1982b) in which a full Kutta condition is included. The accuracy of the theory is fascinating in view of the dramatic simplifications introduced in the theory. For a thick-walled pipe end and a pipe terminated by a horn the end correction behaviour is similar. It is surprising that the nonlinear behaviour at low frequencies and high acoustic amplitudes in the absence of mean flow does not influence the end correction significantly.The aero-acoustic behaviour of the pipe end is dramatially influenced by the presence of a horn. In the presence of a mean flow the horn is a source of sound for a critical range of the Strouhal number.The high accuracy of the experimental data suggests that acoustic measurements can be used for a systematic study of turbulence in unsteady flow and of unsteady flow separation.
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Liu, Yuechang, Xin Zhang, Jianhua Guo, et al. "Tailoring of diversified sound vortices using curved impedance-matched acoustic metasurfaces." Modern Physics Letters B 34, no. 12 (2020): 2050121. http://dx.doi.org/10.1142/s0217984920501213.
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Acoustic vortex beam, which carries the orbital angular momentum, has attracted great interest in recent years. In this paper, we propose a novel curved impedance-matched metasurface constructed with tunable units, which are filled with mixed gases with different refractive indices. It converts an acoustic point source to vortex beam with nearly unity transmittance in a broad frequency bandwidth. By arranging the units, we demonstrate topological charge modulation and rotated direction shifting for acoustic vortex beams. In addition, combining with phase superposition effect, we introduce double curved metasurfaces model. A vortex beam can transform into another vortex beam with different energy flows conveniently. The proposed methods open up an effective avenue for tailoring acoustic vortex fields and provide possibility for applications such as particles trapping, acoustic communication and biomedical engineering.
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Shanbhogue, Santosh J., Michael Seelhorst, and Tim Lieuwen. "Vortex Phase-Jitter in Acoustically Excited Bluff Body Flames." International Journal of Spray and Combustion Dynamics 1, no. 3 (2009): 365–87. http://dx.doi.org/10.1260/175682709789141528.
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This paper describes an experimental study of the effect of acoustic excitation on bluff body stabilized flames, specifically on the flow field characteristics. The Kelvin-Helmholtz (KH) instability of the shear layer is excited due to the incident acoustics. In turn, the KH instability imposes a convecting, harmonic excitation on the flame, which leads to spatially periodic flame wrinkling and heat-release oscillations. Understanding the factors influencing these heat release oscillations requires an understanding of the generation, convection, and dissipation of these vortical disturbances. Phase locked particle image velocimetry was carried out over a range of conditions to characterize the vortical dynamics. It was found that the vortex core location exhibits “phase jitter”, manifested as cycle-to-cycle variation in flame and vorticity field at the same excitation phase. Phase jitter is shown to be a function of separation point dynamics, downstream convection time, and amplitude of acoustic excitation. It leads to fairly significant differences between instantaneous and ensemble averaged flow fields and, in particular, the decay rate of the vorticity in the axial direction.
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Zhong, Siyang, and Xin Zhang. "A generalized sound extrapolation method for turbulent flows." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 474, no. 2210 (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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Liu, FeiFei, ShuJie Jiang, Gang Chen, and Yueming Li. "Numerical Investigation on Vortex-Structure Interaction Generating Aerodynamic Noises for Rod-Airfoil Models." Mathematical Problems in Engineering 2017 (2017): 1–12. http://dx.doi.org/10.1155/2017/3704324.
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In past several decades, vortex-structure interaction generated aerodynamic noise became one of the main concerns in aircraft design. In order to understand the mechanism, the acoustic analogy method combined with the RANS-based nonlinear acoustics solver (NLAS) is investigated. The numerical method is firstly evaluated by the experiment data of the classic rod-airfoil model. Compared with the traditional analogy methods, the RANS/NLAS can capture the nonlinear aerodynamic noise more accurately with lower gird requirements. Then different rod-airfoil configurations were simulated to investigate the aeroacoustic interaction effects. The numerical results are in good agreement with those of the earlier experimental research. It is found that the vortex-shedding crash to the airfoil is the main reason for the noise generation which is dependent on the configurations, distance, and flow conditions.
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Kim, Jin, Eric G. Paterson, and Frederick Stern. "RANS Simulation of Ducted Marine Propulsor Flow Including Subvisual Cavitation and Acoustic Modeling." Journal of Fluids Engineering 128, no. 4 (2005): 799–810. http://dx.doi.org/10.1115/1.2201697.
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High-fidelity Reynolds-averaged Navier Stokes (RANS) simulations are presented for the ducted marine propulsor P5206, including verification and validation (V&V) using available experimental fluid dynamics data, and subvisual cavitation, and acoustics analysis using the modified Rayleigh-Plesset equation along the bubble trajectories with a far-field form of the acoustic pressure for a collapsing spherical bubble. CFDSHIP-IOWA is used with the blended k−ω∕k−ε turbulence model and extensions for a relative rotating coordinate system and overset grids. The intervals of V&V analysis for thrust, torque, and profile averaged radial velocity just downstream of rotor tip are reasonable in comparison with previous results. The flow pattern displays the interaction and merging of the tip-leakage and trailing edge vortices. In the interaction region, multiple peaks and vorticity are smaller, whereas in the merging region, there is better agreement with the experiment. The tip-leakage vortex core position, size, circulation, and cavitation patterns for σi=5 also show good agreement with the experiment, although the vortex core size is larger and the circulation in the interaction region is smaller. The simulations indicate globally minimum Cp=−σi=−8.8 on the suction side of the rotor tip at 84% chord from the leading edge and locally minimum Cp=−6.4 in the tip-leakage vortex at 8% chord downstream of the trailing edge, whereas EFD indicates σi=11 and the location in the tip-leakage vortex core 50% chord downstream of the trailing edge. Subvisual cavitation and acoustics analysis show that bubble dynamics may partly explain these discrepancies.
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Fedoseev, Sergey, and Sergey Timushev. "ON ONE APPROACH TO DETERMINING THE VORTEX SOUND SOURCE." Perm National Research Polytechnic University Aerospace Engineering Bulletin, no. 64 (2021): 43–53. http://dx.doi.org/10.15593/2224-9982/2021.64.05.
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The work consists of five sections and a bibliographic list. The first section provides answers to questions about the relevance, the applied value of the study, as well as the need to develop new approaches that allow modeling vortex structures in engineering practice. In the second section, some mathematical models and approaches used to solve problems of vortex dynamics are considered. The third section is devoted to solving the problem of determining the main parameters of the flow in the core of a vortex ring for given geometric dimensions. It is shown that a turbulent vortex ring is obtained as a result of the interaction of two vortex columns. The fourth section is devoted to methods for characterizing a concentrated vortex as a source of acoustic vibrations. As an object of research, the flow in the core of a turbulent vortex ring is considered. It is assumed that the core of the vortex ring has the shape of a torus. An approach is proposed that makes it possible to establish a strict link between the main flow parameters and the shape of the vortex ring. The aim of this work is to obtain the flow parameters in the core of a vortex ring with their subsequent substitution into the acoustic-vortex equation to analyze the source of acoustic oscillations. It is also necessary to show the presence of a structure in the vortex ring corresponding to some point symmetry and, thus, to abandon the concept of the circular symmetry of the core of the vortex ring. The proposed approach is based on the assertion that a vortex ring can be represented as a set formed according to a “rule” that determines a spatial geometric shape. As a result, an approach was proposed for analyzing the vortex ring as a source of acoustic oscillations, and it was also formulated and theoretically substantiated that the core of a turbulent vortex ring having the shape of a torus can be considered as a result of the interaction of two vortex columns.
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Kambe, T. "Acoustic emissions by vortex motions." Journal of Fluid Mechanics 173 (December 1986): 643–66. http://dx.doi.org/10.1017/s0022112086001301.
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Fundamental aspects of the acoustic emission by vortex motions are considered by summarizing our recent work. Three typical cases are presented as illustrative examples: (i) head-on collision of two vortex rings, (ii) a vortex ring moving near a circular cylinder, and (iii) a vortex ring moving near a sharp edge of a semi-infinite plate. The theory of aerodynamic sound for low-Mach-number motion of an inviscid fluid predicts that the amplitude of the acoustic pressure in the far field is proportional to U4, U3 and U2.5 for (i)-(iii) respectively, where U is the translation velocity of a single vortex ring. Therefore the vortex-edge interaction generates the most powerful sound among the three cases at low Mach numbers. Our observations have confirmed these scaling laws. In addition to the scaling properties, we show the wave profiles of the emission as well as the directionality pattern. The head-on collision radiates waves of quadrupole directionality, whereas waves of dipole property are originated by the vortex-cylinder interaction. The third, vortex-edge, interaction generates waves of a cardioid directionality pattern. The wave profiles of all three cases are related to the time derivatives of the volume flux (through the vortex ring) of an imaginary potential flow which is characteristic of each configuration, although the orders of the time derivatives are different for each case. The observed profiles are surprisingly well fitted to the curves predicted by the theory, except the final period of the first case, in which viscosity is assumed to play an important role. The observed wave profiles are shown in a perspective diagram.
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Weyna, Stefan, Witold Mickiewicz, Michał Pyła, and Michał Jabłoński. "Experimental Acoustic Flow Analysis Inside a Section of an Acoustic Waveguide." Archives of Acoustics 38, no. 2 (2013): 211–16. http://dx.doi.org/10.2478/aoa-2013-0025.
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Abstract Noise propagation within ducts is of practical concern in many areas of industrial processes where a fluid has to be transported in piping systems. The paper presents experimental data and visualization of flow in the vicinity of an abrupt change in cross-section of a circular duct and on obstacles inside where the acoustic wave generates nonlinear separated flow and vortex fields. For noise produced by flow wave of low Mach number, laminar and turbulent flows are studied us- ing experimental sound intensity (SI) and laser particle image velocimetry (PIV) technique adopted to acoustics (A-PIV). The emphasis is put on the development and application of these methods for better understanding of noise generation inside the acoustic ducts with different cross-sections. The intensity distribution inside duct is produced by the action of the sum of modal pressures on the sum of modal particle velocities. However, acoustic field is extremely complicated because pressures in non-propagating (cut-off) modes cooperate with particle velocities in propagating modes, and vice versa. The discrete frequency sound is strongly influenced by the transmission of higher order modes in the duct. By under- standing the mechanism of energy in the sound channels and pipes we can find the best solution to noise abatement technology. In the paper, numerous methods of visualization illustrate the vortex flow as an acoustic velocity or sound intensity stream which can be presented graphically. Diffraction and scattering phenomena occurring inside and around the open-end of the acoustic duct are shown.
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Stenflo, L. "Acoustic gravity vortex chains." Physics Letters A 186, no. 1-2 (1994): 133–34. http://dx.doi.org/10.1016/0375-9601(94)90933-4.
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Samanta, Arnab, and Jonathan B. Freund. "A model supersonic buried-nozzle jet: instability and acoustic wave scattering and the far-field sound." Journal of Fluid Mechanics 778 (July 30, 2015): 189–215. http://dx.doi.org/10.1017/jfm.2015.354.
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We consider sound source mechanisms involving the acoustic and instability modes of dual-stream isothermal supersonic jets with the inner nozzle buried within an outer shroud-like nozzle. A particular focus is scattering into radiating sound waves at the shroud lip. For such jets, several families of acoustically coupled instability waves exist, beyond the regular vortical Kelvin–Helmholtz mode, with different shapes and propagation characteristics, which can therefore affect the character of the radiated sound. In our model, the coaxial shear layers are vortex sheets while the incident acoustic disturbances are the propagating shroud modes. The Wiener–Hopf method is used to compute their scattering at the sharp shroud edge to obtain the far-field radiation. The resulting far-field directivity quantifies the acoustic efficiency of different mechanisms, which is particularly important in the upstream direction, where the results show that the scattered sound is more intense than that radiated directly by the shear-layer modes.
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Perry, Spencer B., and Kent L. Gee. "The Acoustically Driven Vortex Cannon." Physics Teacher 52, no. 3 (2014): 146–47. http://dx.doi.org/10.1119/1.4865515.
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LEBLANC, STÉPHANE. "Destabilization of a vortex by acoustic waves." Journal of Fluid Mechanics 414 (July 10, 2000): 315–37. http://dx.doi.org/10.1017/s0022112000008612.
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The linear stability of a circular vortex interacting with two plane acoustic waves propagating in opposite directions is investigated. When the wavelength is large compared to the size of the vortex, the core is subjected to time-periodic compressions and strains. A stability analysis is performed with the geometrical optics approximation, which considers short-wavelength perturbations evolving along the trajectories of the basic flow. On the vortex core, the problem is reduced to a single Hill–Schrödinger equation with periodic or almost-periodic potential, the solution to which grows exponentially when parametric resonances occur. On interacting with the acoustic waves, the circular vortex is thus unstable to three-dimensional perturbations.
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Clair, Vincent, and Gwénaël Gabard. "Spectral broadening of acoustic waves by convected vortices." Journal of Fluid Mechanics 841 (February 19, 2018): 50–80. http://dx.doi.org/10.1017/jfm.2018.94.
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The scattering of acoustic waves by a moving vortex is studied in two dimensions to bring further insight into the physical mechanisms responsible for the spectral broadening caused by a region of turbulence. When propagating through turbulence, a monochromatic sound wave will be scattered over a range of frequencies, resulting in typical spectra with broadband sidelobes on either side of the tone. This spectral broadening, also called ‘haystacking’, is of importance for noise radiation from jet exhausts and for acoustic measurements in open-jet wind tunnels. A semianalytical model is formulated for a plane wave scattered by a vortex, including the influence of the convection of the vortex. This allows us to perform a detailed parametric study of the properties and evolution of the scattered field. A time-domain numerical model for the linearised Euler equations is also used to consider more general sound fields, such as that radiated by a point source in a uniform flow. The spectral broadening stems from the combination of the spatial scattering of sound due to the refraction of waves propagating through the vortex, and two Doppler shifts induced by the motion of the vortex relative to the source and of the observer relative to the vortex. The fact that the spectrum exhibits sidebands is directly explained by the directivity of the scattered field which is composed of several beams radiating from the vortex. The evolution of the acoustic spectra with the parameters considered in this paper is compared with the trends observed in previous experimental work on acoustic scattering by a jet shear layer.
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Martini, Eduardo, André V. G. Cavalieri, and Peter Jordan. "Acoustic modes in jet and wake stability." Journal of Fluid Mechanics 867 (March 28, 2019): 804–34. http://dx.doi.org/10.1017/jfm.2019.148.
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Motivated by recent studies that have revealed the existence of trapped acoustic waves in subsonic jets (Towne et al., J. Fluid Mech., vol. 825, 2017, pp. 1113–1152), we undertake a more general exploration of the physics associated with acoustic modes in jets and wakes, using a double vortex-sheet model. These acoustic modes are associated with eigenvalues of the vortex-sheet dispersion relation; they are discrete modes, guided by the vortex sheet; they may be either propagative or evanescent; and under certain conditions they behave in the manner of acoustic-duct modes. By analysing these modes we show how jets and wakes may both behave as waveguides under certain conditions, emulating ducts with soft or hard walls, with the vortex-sheet impedance providing effective ‘wall’ conditions. We consider, in particular, the role that upstream-travelling acoustic modes play in the dispersion-relation saddle points that underpin the onset of absolute instability. The analysis illustrates how departure from duct-like behaviour is a necessary condition for absolute instability, and this provides a new perspective on the stabilising and destabilising effects of reverse flow, temperature ratio and compressibility; it also clarifies the differing symmetries of jet (symmetric) and wake (antisymmetric) instabilities. An energy balance, based on the vortex-sheet impedance, is used to determine stability conditions for the acoustic modes: these may become unstable in supersonic flow due to an energy influx through the shear layers. Finally, we construct the impulse response of flows with zero and finite shear-layer thickness. This allows us to show how the long-time wavepacket behaviour is indeed determined by interaction between Kelvin–Helmholtz and acoustic modes.
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ZHENG, TING-HUI, GEORGIOS H. VATISTAS, and ALEX POVITSKY. "SOUND GENERATION BY ONE-CELL AND TWO-CELL VORTICES IN A NONUNIFORM FLOW." Journal of Computational Acoustics 14, no. 03 (2006): 321–37. http://dx.doi.org/10.1142/s0218396x06003074.
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Sound generation by vortical disturbance in a subsonic flow around a cylinder is investigated, using different vortex formulations, by solving both linearized and nonlinear Euler equations numerically. Numerical errors associated with the finite-difference discretization and boundary conditions are kept small using the high-order-accurate spatial differentiation and time marching schemes along with accurate nonreflecting boundary conditions and the sponge layer. If the radial velocity in vortex is assumed equal to zero, the intensity and directivity of acoustic wave patterns appear to be quite similar for all vortex models. If the radial velocity is taken into consideration, for single-cell vortex, there is no noticeable change happening to the acoustic wave; for two-cell vortex, although the radial velocity is still much smaller than the tangential velocity, the former plays an important role in generation and propagation of nonsymmetrical sound waves. If only initial tangential velocity or only initial radial velocity of the two-cell vortical flow disturbance is considered, the generated sound level would increase with the Mach number of mean flow while the angular distribution of sound directivity remains the same. If the two-cell vortex with both velocity components is considered, the Mach number of the background flow would change not only the amplitude of the acoustic pressure but also the directivity of sound. As the Mach number increases, the maximum amplitude of acoustic pressure will be shifted to the upper half-plane.
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RIVOALEN, ELIE, SERGE HUBERSON, and OMAR M. KNIO. "NUMERICAL STUDY OF SOUND RADIATION BY AXISYMMETRIC VORTEX RINGS." Journal of Computational Acoustics 11, no. 01 (2003): 11–45. http://dx.doi.org/10.1142/s0218396x03001808.
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The sound production by vortex rings is investigated by means of an axisymmetric vortex particle method. The predictions are first calibrated by analyzing the noise generated by steady vortex rings that are described by the analytical solutions of Fraenkel and Norbury. The noise produced by isolated vortex rings for both nominally steady and unsteady cores is then analyzed. For nominally steady cores, computed results indicate that the efficiency of sound radiation decreases as the slenderness parameter is reduced, and the acoustic signals reveal a dominant period that is approximately half the eddy turnover time. For unsteady cores, the amplitude of the radiated sound is substantially higher than that of similar steady rings. When the initial core vorticity distribution is nonuniform, complex internal motion may also occur within the core which is also reflected in the corresponding far-field acoustic signal. Finally, the effect of vortex stretching is analyzed based on computations of two coaxial corotating vortex rings.
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Poinsot, Thierry J., Arnaud C. Trouve, Denis P. Veynante, Sebastien M. Candel, and Emile J. Esposito. "Vortex-driven acoustically coupled combustion instabilities." Journal of Fluid Mechanics 177 (April 1987): 265–92. http://dx.doi.org/10.1017/s0022112087000958.
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Combustion instability is investigated in the case of a multiple inlet combustor with dump. It is shown that low-frequency instabilities are acoustically coupled and occur at the eigenfrequencies of the system. Using spark-schlieren and a special phase-average imaging of the C2-radical emission, the fluid-mechanical processes involved in a vortex-driven mode of instability are investigated. The phase-average images provide maps of the local non-steady heat release. From the data collected on the combustor the processes of vortex shedding, growth, interactions and burning are described. The phases between the pressure, velocity and heat-release fluctuations are determined. The implications of the global Rayleigh criterion are verified and a mechanism for low-frequency vortex-driven instabilities is proposed.
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Leblanc, Stéphane. "Acoustic excitation of vortex instabilities." Physics of Fluids 13, no. 11 (2001): 3496–99. http://dx.doi.org/10.1063/1.1406935.
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Popescu, Mihaela, Stein Tore Johansen, and Wei Shyy. "Flow-Induced Acoustics in Corrugated Pipes." Communications in Computational Physics 10, no. 1 (2011): 120–39. http://dx.doi.org/10.4208/cicp.301209.230710a.
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AbstractWhen gas flows through corrugated pipes, pressure waves interacting with vortex shedding can produce distinct tonal noise and structural vibration. Based on established observations, a model is proposed which couples an acoustic pipe and self-excited oscillations with vortex shedding over the corrugation cavities. In the model, the acoustic response of the corrugated pipe is simulated by connecting the lossless medium moving with a constant velocity with a source based on a discrete distribution of van der Pol oscillators arranged along the pipe. Our time accurate solutions exhibit dynamic behavior consistent with that experimentally observed, including the lock-in frequency of vortex shedding, standing waves and the onset fluid velocity capable of generating the lock-in.
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STRAWN, ROGER C., RUPAK BISWAS, and ANASTASIOS S. LYRINTZIS. "HELICOPTER NOISE PREDICTIONS USING KIRCHHOFF METHODS." Journal of Computational Acoustics 04, no. 03 (1996): 321–39. http://dx.doi.org/10.1142/s0218396x96000106.
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This paper presents two methods for predicting the noise from helicopter rotors in forward flight. Aerodynamic and acoustic solutions in the near field are computed with a finite-difference solver for the Euler equations. Two different Kirchhoff acoustics methods are then used to propagate the acoustic signals to the far field in a computationally-efficient manner. One of the methods uses a Kirchhoff surface that rotates with the rotor blades. The other uses a nonrotating Kirchhoff surface. Results from both methods are compared to experimental data for both high-speed impulsive noise and blade-vortex interaction noise. Agreement between experimental data and computational results is excellent for both cases. The rotating and nonrotating Kirchhoff methods are also compared for accuracy and efficiency. Both offer high accuracy with reasonable computer resource requirements. The Kirchhoff integrations efficiently extend the near-field finite-difference results to predict the far field helicopter noise.
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Ivanov, Evgeniy Gennadievich, Boris Ivanovich Gorbunov, Alexander Valentinovich Pasin, Boris Alexandrovich Aryutov, and Alexei Ivanovich Novozhilov. "Augmentation of Vortex Cavitator Performance by the Use of Co-Directional Swirl of the Flux after Vortex Chamber." Progress in Agricultural Engineering Sciences 15, no. 1 (2019): 1–22. http://dx.doi.org/10.1556/446.15.2019.1.1.
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Abstract Background: Acoustic cavitation is the creation and collapse of cavitation caverns in liquid in an acoustic field with a frequency of f = 1–3 kHz. The acoustic-cavitation processes manifest themselves during the collapse phase, with high pressure gradient continuum deformation, with a multiple transformation of energy forms. Liquid whistles are widely used to create an acoustic field of high power, but their efficiency only reaches 6–12%. We propose a liquid whistle in the form of a vortex cavitator (analogue of the Ranque vortex tube) with a rotating body in which a reduction in the input power is predicted. Objective: Verification of feasibility of using a rotating body in a vortex cavitator with a rotation co-directional to the operational pump impeller. Method: The method for identifying the feasibility of using a rotating body is to exclude body from the prototype and directly connect vortex chamber outlet with the pump inlet, which ensures the most complete preservation of co-directional vortex component of the flux entering the pump impeller. Results: The results of experimental studies confirmed the validity of the hypothesis to a greater extent, since we achieved an increase in pressure at the outlet of the pump and a decrease in power at the drive relative to the original design. Conclusions: The feasibility of designing the vortex cavitator body with rotation capability has been established, which will provide a reduction in input power of at least 30% by a rotation of the body, co-directional with the impeller.
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HATTORI, Y., and STEFAN G. LLEWELLYN SMITH. "Axisymmetric acoustic scattering by vortices." Journal of Fluid Mechanics 473 (December 10, 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.