183 results on '"vortex"'
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2. Modeling the Non-Incidence Inlet Flow Rate Coefficient in a Centrifugal Compressor Impeller.
- Author
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Drozdov, A. A. and Galerkin, Y. B.
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GAS dynamics , *CENTRIFUGAL compressors , *MECHANICAL loads , *COMPUTATIONAL fluid dynamics , *IMPELLERS - Abstract
Non-incidence flow rate determination is necessary in the calculation of gas-dynamic characteristics of a centrifugal compressor by the Universal Modeling Method, since the magnitude of incidence losses depends on this. The direction of the critical streamline is affected by the decrease in the flow area by the blades of finite thickness and the load of the blades. In the course of primary design, the Universal Modeling Method uses a scheme of replacing the influence of the blade load with the effect of a vortex with identical circulation. Finally, the value of the inlet blade angle is selected by calculating the inviscid flow around the blades. For impellers with small design flow coefficients, the condition of the non-incidence inlet for the primary design and for the calculation of the inviscid flow is significantly different. The correctness of the calculation of the non-incidence regime for non-viscous flow was checked earlier by measurements of the flow in the impellers. CFD calculations and no-viscid calculations of twenty impellers were made in a tenfold range of design flow coefficients. The identity of inlet conditions by both methods was shown. To increase the accuracy of the primary design, the calculation model was refined. An empirical coefficient is introduced into the formula for calculating the velocity induced by the vortex. The analysis of data for 32 impellers with different blade profiling allowed to propose out formulae for calculating empirical coefficient, depending on the type of impeller, the blade load and the width of the throat at an impeller inlet. The calculation based on the new scheme with the empirical coefficient is accurate enough for the primary design. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
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3. Spatiotemporal vortex rings in atomic Bose–Einstein condensates.
- Author
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Chelpanova, O. G., Kuriatnikov, Y. I., Vilchinskii, S., and Yakimenko, A. I.
- Subjects
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BOSE-Einstein condensation , *EDGE dislocations , *SPACETIME - Abstract
We investigate spatiotemporal vortex rings with phase dislocation both in space and time. It is demonstrated that these structures naturally appear as a periodical in time edge phase dislocation at the low-density region of a perturbed atomic Bose–Einstein condensate. The condition of formation, dynamics and stability of the spatiotemporal vortex rings are investigated for repulsive and attractive interatomic interactions. These theoretical findings open up a perspective for experimental observation of novel type of topological coherent structures in ultracold gases. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
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4. Diffusive instabilities of baroclinic lenticular vortices
- Author
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Oleg N. Kirillov and Joris Labarbe
- Subjects
F300 ,Baroclinity ,Computational Mechanics ,FOS: Physical sciences ,Dynamical Systems (math.DS) ,Instability ,Physics - Geophysics ,Rossby number ,Singularity ,Dispersion relation ,FOS: Mathematics ,Mathematics - Dynamical Systems ,Mathematical Physics ,Fluid Flow and Transfer Processes ,Physics ,Mechanical Engineering ,Schmidt number ,Fluid Dynamics (physics.flu-dyn) ,Equations of motion ,Mathematical Physics (math-ph) ,Physics - Fluid Dynamics ,Mechanics ,Condensed Matter Physics ,Geophysics (physics.geo-ph) ,Vortex ,Physics - Atmospheric and Oceanic Physics ,Mechanics of Materials ,Atmospheric and Oceanic Physics (physics.ao-ph) - Abstract
We consider a model of a circular lenticular vortex immersed into a deep and vertically stratified viscous fluid in the presence of gravity and rotation. The vortex is assumed to be baroclinic with a Gaussian profile of angular velocity both in the radial and axial directions. Assuming the base state to be in a cyclogeostrophic balance, we derive linearized equations of motion and seek for their solution in a geometric optics approximation to find amplitude transport equations that yield a comprehensive dispersion relation. Applying algebraic Bilharz criterion to the latter, we establish that stability conditions are reduced to three inequalities that define stability domain in the space of parameters. The main destabilization mechanism is either stationary or oscillatory axisymmetric instability depending on the Schmidt number ($Sc$), vortex Rossby number and the difference between the radial and axial density gradients as well as the difference between the epicyclic and vertical oscillation frequencies. We discover that the boundaries of the regions of stationary and oscillatory axisymmetric instabilities meet at a codimension-2 point, forming a singularity of the neutral stability curve. We give an exhaustive classification of the geometry of the stability boundary, depending on the values of the Schmidt number. Although we demonstrate that the centrifugally stable (unstable) Gaussian lens can be destabilized (stabilized) by the differential diffusion of mass and momentum and that destabilization can happen even in the limit of vanishing diffusion, we also describe explicitly a set of parameters in which the Gaussian lens is stable for all $Sc>0$.
- Published
- 2021
5. Vortex reconnections between coreless vortices in binary condensates.
- Author
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Gautam, S., Suthar, K., and Angom, D.
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VORTEX methods , *VORTEX motion , *MAGNETIC reconnection , *TURBULENT flow , *SUPERFLUIDITY , *DILUTE magnetic materials , *GAS dynamics - Abstract
Vortex reconnections plays an important role in the turbulent flows associated with the superfluids. To understand the dynamics, we examine the reconnections of vortex rings in the superfluids of dilute atomic gases confined in trapping potentials using Gross-Petaevskii equation. Further more we study the reconnection dynamics of coreless vortex rings, where one of the species can act as a tracer. [ABSTRACT FROM AUTHOR]
- Published
- 2014
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6. Alignment and rotation of spheroids in unsteady vortex flow
- Author
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Helge I. Andersson, Rohith Jayaram, Lihao Zhao, Jurriaan J. J. Gillissen, and Y. Jie
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Fluid Flow and Transfer Processes ,Preferential alignment ,Physics ,Homogeneous isotropic turbulence ,Mechanical Engineering ,Computational Mechanics ,Laminar flow ,Mechanics ,Vorticity ,Condensed Matter Physics ,Rotation ,01 natural sciences ,010305 fluids & plasmas ,Vortex ,Physics::Fluid Dynamics ,Flow (mathematics) ,Mechanics of Materials ,Inviscid flow ,0103 physical sciences ,010306 general physics - Abstract
Preferential orientations of inertialess nonspherical particles are examined through three qualitatively different stages of a time-evolving Taylor–Green vortex flow. Despite an unexpected decorrelation between the vorticity vector and the direction of Lagrangian stretching, experienced by material fluid elements over a substantial time interval, prolate spheroids aligned with the Lagrangian stretching direction, whereas oblate spheroids aligned with the Lagrangian compression direction. We, therefore, infer that spheroidal tracers orient themselves relative to the Lagrangian history of the velocity gradients, defined by the left Cauchy–Green deformation tensor, rather than with the fluid vorticity vector. This preferential alignment persists all throughout the statistically unsteady flow field and even in the inviscid and nonturbulent early stage of the time-dependent vortex flow. This explains the observed preferential spinning of rods and tumbling of disks, similar to that in homogeneous isotropic turbulence, even at the early stage when the flow is anisotropic and laminar. These preferred modes of particle rotation prevail all through the evolving flow despite a surprisingly long time interval, during which the fluid vorticity decorrelates from the direction of Lagrangian stretching. This is the authors’ accepted and refereed manuscript to the article. This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. The following article appeared in Physics of Fluids and may be found at https://doi.org/10.1063/5.0041290
- Published
- 2021
7. A Python implementation in graphic processing unit of a lattice Boltzmann model for unstable three-dimensional flows in immersed permeable media
- Author
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Nicolas Silin, Alejandro Clausse, and G. Boroni
- Subjects
Lattice boltzmann model ,Computational Mechanics ,01 natural sciences ,010305 fluids & plasmas ,0103 physical sciences ,Permeable media ,010306 general physics ,computer.programming_language ,Fluid Flow and Transfer Processes ,Physics ,Mechanical Engineering ,Three dimensional flow ,Mechanics ,Immersed boundary method ,Python (programming language) ,Condensed Matter Physics ,Lattice Boltzmann ,Vortex ,purl.org/becyt/ford/2 [https] ,Mechanics of Materials ,Drag ,purl.org/becyt/ford/2.3 [https] ,Transport phenomena ,Porous medium ,computer ,Python - Abstract
The implementation of a lattice Boltzmann model for three-dimensional permeable media with localized drag forces is presented. The model was previously introduced for two-dimensional geometries and follows the basics of the immersed boundary method. Permeable flows are much less stable than their counterparts in porous media and generally produce large coherent flow structures, such as vortex lines, rolls, and wakes. In addition, in permeable media, the small-scale geometry often needs to be represented to a high degree of detail in order to capture certain transport phenomena, such as micro-convection or pollination. Hence, both calculation speed and memory requirements are under strain. The present model was implemented in a graphic processing unit showing excellent performance in the calculation of stable and unstable flows in a rectangular channel partially obstructed by an array of parallel wires. In particular, the model is able to deal with small and medium spatial scales without losing the heterogeneous nature of permeable flows in the homogenization process. The algorithm to manage memory issues is described in detail, and the results of the test case for stable and unstable conditions show the capability of the method to simulate these types of flows. Fil: Boroni, Gustavo Adolfo. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Sociales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Silin, Nicolas. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Clausse, Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica; Argentina
- Published
- 2020
8. Role of Plasma Electron Vortex Formation at Laser Interaction with Foil for Ion Acceleration.
- Author
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Maslov, V. I., Egorov, A. M., and Onishchenko, I. N.
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ELECTRON distribution , *PLASMA electrodynamics , *ELECTROMAGNETIC fields , *MAGNETOHYDRODYNAMICS , *PLASMA dynamics - Abstract
The distribution of electrical potential and electron density near foil, resulting to vortical electron dynamics at interaction of an intensive laser pulse with a foil, is considered. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
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9. Equilibrium Interface Position During Operation of a Fixed Cylinder Vortex Separator.
- Author
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Gaul, Logan, Papas, Zachary, Kurwitz, Cable, and Best, Frederick R.
- Subjects
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REDUCED gravity environments , *LIFE support systems (Space environment) , *CRITICAL care medicine , *ENVIRONMENTAL engineering , *VORTEX separation process (Water purification) - Abstract
Microgravity separation is a critical need for the development of high performance thermal management and advanced life support systems. Texas A&M has been working in the area of vortex separation for several years (Carron and Best, 1991; Kurwitz and Best, 2000). Recent reduced gravity flight data has been analyzed to compare the interface position and shape as a function of liquid inventory and rotational speed. A comparison of the measured interface location with the interface shape predicted from irrotational flow resulted in a RMSD of 0.45 cm and the RMSD of the measured interface location to an interface determined assuming that the gas forms a right circular cylinder centrally located in the separator was 0.7015. The accuracy of the prediction method is better at higher rotational speeds corresponding to larger flow rates. The high degree of fidelity between the measured interface location with that predicted using a simple irrotational flow assumption indicates that secondary flows are small in magnitude compared to the rotational flow of liquid and provides a high degree of confidence in the prediction of reduced gravity performance. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
10. Microscopic solitons in correlated electronic systems: theory versus experiment.
- Author
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Brazovskii, S.
- Subjects
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SOLITONS , *ELECTRONIC systems , *DENSITY wave theory , *PERMITTIVITY , *FERROELECTRIC crystals - Abstract
Symmetry broken electronic states give rise to topological defects: from extended domain walls—“stripes” as solitonic lattices to microscopic solitons as anomalous quasi-particles and instantons in their dynamics. We shall collect and interpret experimental evidences on existence of microscopic solitons, and their determining role in electronic processes of quasi-1D electronic crystals. Thus, the ferroelectric charge ordering in organic conductors gives access to several types of solitons observed in conductivity (holons) and in permittivity (polar kinks), to solitons’ bound pairs in optics, to compound charge-spin solitons. In charge density waves, the individual phase solitons have been visually captured in recent STM experiments. The resolved subgap tunneling spectra recover these solitons (in aggregated form of dislocations in statics and as instantons—the phase slips in dynamics), as well as the amplitude kinks—the spinons. The theory relies upon the regime of quantum dissipation provided by soft mode emittance in the course of the soliton creation, and on effects of dimensional crossover. With onset of a 2D or a 3D long range order, the topologically nontrivial solitons experience the confinement resulting in the spin-charge recombination. It originates the symmetry broken spin-or charge- roton configurations with charge- or spin- kinks localized in the core, correspondingly for cases of repulsion and attraction. These complex excitations can be viewed as nucleuses of the melted stripe phases, which appears in doped antiferromagnetic—Mott insulators or in spin-polarized superconductors and charge density waves. [ABSTRACT FROM AUTHOR]
- Published
- 2009
- Full Text
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11. Interaction between vortices and nuclei in the inner crust of neutron stars.
- Author
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Avogadro, P., Barranco, F., Broglia, R. A., and Vigezzi, E.
- Subjects
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NUCLEAR reactions , *HADRON-nuclei interactions , *NEUTRONS , *PARTICLES (Nuclear physics) , *NUCLEAR physics - Abstract
The inner crust of a neutron star is expected to contain a Coulomb lattice of nuclei immersed in a superfluid sea of free neutrons. The rotation of the star induces the formation of vortices in the neutron sea, whose dynamics is influenced by the interaction with the nuclei. In particular, this interaction is important to determine whether it is energetically advantageous for vortices to pin on nuclei or not. We find that the pinning energy is sensitive to quantal size effects. In fact, the nuclear shell structure tends to hinder the formation of vortices inside the nuclear volume. [ABSTRACT FROM AUTHOR]
- Published
- 2009
- Full Text
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12. 39 Questionable Assumptions in Modern Physics.
- Author
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Volk, Greg
- Subjects
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NUCLEAR physics , *NUCLEAR reactions , *NUCLEAR energy , *COLLISIONS (Nuclear physics) , *STRING models (Physics) - Abstract
The growing body of anomalies in new energy, low energy nuclear reactions, astrophysics, atomic physics, and entanglement, combined with the failure of the Standard Model and string theory to predict many of the most basic fundamental phenomena, all point to a need for major new paradigms. Not Band-Aids, but revolutionary new ways of conceptualizing physics, in the spirit of Thomas Kuhn’s The Structure of Scientific Revolutions. This paper identifies a number of long-held, but unproven assumptions currently being challenged by an increasing number of alternative scientists. Two common themes, both with venerable histories, keep recurring in the many alternative theories being proposed: (1) Mach’s Principle, and (2) toroidal, vortex particles. Matter-based Mach’s Principle differs from both space-based universal frames and observer-based Einsteinian relativity. Toroidal particles, in addition to explaining electron spin and the fundamental constants, satisfy the basic requirement of Gauss’s misunderstood B Law, that motion itself circulates. Though a comprehensive theory is beyond the scope of this paper, it will suggest alternatives to the long list of assumptions in context. [ABSTRACT FROM AUTHOR]
- Published
- 2009
- Full Text
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13. Evolution of Quantum Systems from Microscopic to Macroscopic Scales.
- Author
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Ovchinnikov, Sergey Y., Macek, Joseph H., Sternberg, James S., Lee, Teck-Ghee, and Schultz, David R.
- Subjects
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QUANTUM scattering , *QUANTUM theory , *MICROSCOPICAL technique , *ELECTRONIC systems , *ANGULAR momentum (Nuclear physics) , *DISTRIBUTION (Probability theory) - Abstract
Even though the static properties of quantum systems have been known since the early days of quantum mechanics, accurate simulation of the dynamical break-up or ionization remains a theoretical challenge despite our complete knowledge of the relevant interactions. Simulations are challenging because of highly oscillatory exponential phase factors in the electronic wave function and the infinitesimally small values of the continuum components of electronic probability density at large times after the collision. The approach we recently developed, the regularized time-dependent Schrödinger equation method, has addressed these difficulties by removing the diverging phase factors and transforming the time-dependent Schrödinger equation to an expanding space. The evolution of the electronic wave function was followed to internuclear distances of R = 100,000 a.u. or 5 microns, which is of the order of the diameter of a human hair. Our calculations also revealed unexpected presence of free vortices in the electronic wave function. The discovered vortices also bring new light on the mechanism of transferring of the angular momentum from an external to internal motion. The connection between the observable momentum distribution and the time-dependent wave function implies that vortices in the wave function at large times are imaged in the momentum distribution. [ABSTRACT FROM AUTHOR]
- Published
- 2009
- Full Text
- View/download PDF
14. Vortex Formation in a Plasma Interacting with Neutral Flow.
- Author
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Tanaka, M. Y., Aramaki, M., Ogiwara, K., Etoh, S., Yoshimura, S., and Varanjes, J.
- Subjects
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VORTEX motion , *ELECTRIC fields , *IONS , *PLASMA gases , *SPECTRUM analysis , *FLUORESCENCE - Abstract
Recently, it has been observed that there exists a class of vortices which rotates in the opposite direction to E×B drift (referred to as anti-E×B vortex). This result suggests that a predominant force other than electric field is acting on ions. It is found that momentum transport and resultant force generation through the interaction between ions and neutral flow play an essential role on anti-E×B vortex formation. The existence of inward neutral flow, which drives the ions in the anti-E×B direction, has been confirmed using a newly-developed high-resolution laser induced fluorescence (LIF) spectroscopy system. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
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15. Single Spin Asymmetry in Strongly Correlated Quark Model.
- Author
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Musulmanbekov, G.
- Subjects
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QUARK models , *ROTATIONAL motion , *VORTEX motion , *NUCLEAR models , *COLLISIONS (Nuclear physics) , *PARTICLES (Nuclear physics) - Abstract
The Single Transverse — Spin Asymmetry (SSA) is analysed in the framework of the Strongly Correlated Quark Model proposed by author, where the proton spin emerges from the orbital momenta of quark and qluon condensates circulating around the valence quarks. It is shown that dominating factors of appearance of SSA are the orbiting around the valence quarks sea quark and qluon condensates and spin dependent quark-quark cross sections. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]
- Published
- 2007
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16. Symmetry Breaking in Bose-Einstein Condensates.
- Author
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Ueda, Masahito, Kawaguchi, Yuki, Saito, Hiroki, Kanamoto, Rina, and Nakajima, Tatsuya
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SYMMETRY breaking , *SOLITONS , *NONLINEAR theories , *BOSE-Einstein condensation , *BOSONS , *MESOSCOPIC phenomena (Physics) - Abstract
A gaseous Bose-Einstein condensate (BEC) offers an ideal testing ground for studying symmetry breaking, because a trapped BEC system is in a mesoscopic regime, and situations exist under which symmetry breaking may or may not occur. Investigating this problem can explain why mean-field theories have been so successful in elucidating gaseous BEC systems and when many-body effects play a significant role. We substantiate these ideas in four distinct situations: namely, soliton formation in attractive BECs, vortex nucleation in rotating BECs, spontaneous magnetization in spinor BECs, and spin texture formation in dipolar BECs. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]
- Published
- 2006
- Full Text
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17. Onset of Turbulence in Superfluid 3He-B and its Dependence on Vortex Injection in Applied Flow.
- Author
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Finne, A. P., Blaauwgeers, R., Boldarev, S., Eltsov, V. B., Kopu, J., and Krusius, M.
- Subjects
- *
VORTEX motion , *GASES at high temperatures , *NUCLEAR magnetic resonance , *DAMPING rings (Nuclear physics) , *SUPERFLUIDITY , *LIQUID helium , *TURBULENCE , *FLOW injection analysis - Abstract
Vortex dynamics in 3He-B is divided by the temperature dependent damping into a high-temperature regime, where the number of vortices is conserved, and a low-temperature regime, where rapid vortex multiplication takes place in a turbulent burst. We investigate experimentally the hydrodynamic transition between these two regimes by injecting seed vortex loops into vortex-free rotating flow. The onset temperature of turbulence is dominated by the roughly exponential temperature dependence of vortex friction, but its exact value is found to depend on the injection method. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]
- Published
- 2006
- Full Text
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18. Specific Heat Measurements of Mesoscopic Loops.
- Author
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Bourgeois, O., Ong, F., Skipetrov, S. E., and Chaussy, J.
- Subjects
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SPECIFIC heat , *MESOSCOPIC phenomena (Physics) , *LOW temperatures , *ELECTRON beam lithography , *MAGNETIC fields , *SUPERCONDUCTIVITY , *THERMODYNAMICS , *NANOSTRUCTURES - Abstract
We report highly sensitive specific heat measurements on mesoscopic superconducting loops at low temperature. These mesoscopic systems exhibit thermal properties significantly different from that of the bulk materials. The measurement is performed on a silicon membrane sensor where 450 000 superconducting aluminium loops are deposited through electron beam lithography, under an applied magnetic field. Each entry of a vortex is associated to a jump in the specific heat of few thousands of Boltzmann constant kB indicating the existence of phase transitions. The periodicity of this sequential phase transitions is a nontrivial behaviour and varies strongly as the temperature is decreased. The successive phase transitions are well described by the Ginzburg-Landau theory of superconductivity. The presence of metastable states is responsible for the n[uppercase_phi_synonym]0 (n=1, 2, 3...) periodicity of the discontinuities of the measured specific heat. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]
- Published
- 2006
- Full Text
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19. Ovsyannikov Vortex: Theory and Applications to Model of Hurricane.
- Author
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Cherevko, A. A. and Chupakhin, A. P.
- Subjects
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GAS dynamics , *FLUID dynamics , *HURRICANES , *VORTEX motion , *HYDRODYNAMICS - Abstract
The new exact solution of gas dynamics equation, called Ovsyannikov vortex, is investigated. It is the generalization of radial symmetrical solutions. These solutions describe gas source with nonzero curl. The applications for simulation of hurricanes are discussed. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]
- Published
- 2006
- Full Text
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20. QCD, hadrons and beyond.
- Author
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Nardulli, G.
- Subjects
- *
QUANTUM chromodynamics , *HADRONS , *YANG-Mills theory , *SUPERSYMMETRY , *QUARK confinement , *SPECTRUM analysis - Abstract
I give a summary of Section E of the sixth edition of the Conference Quark confinement and the hadron spectrum. Papers were presented on different subjects, from spectroscopy, including pentaquarks and hadron structure, to new physics effects (non commutative field theories, supersymmetry and extra dimensions) and the problem of color confinement, both in ordinary Yang-Mills models and in supersymmetric Yang-Mills. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]
- Published
- 2005
- Full Text
- View/download PDF
21. Magnetic droplet solitons
- Author
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Andrew D. Kent, Ferran Macià, Department of Energy (US), Ministerio de Economía y Competitividad (España), Ministerio de Ciencia, Innovación y Universidades (España), and National Science Foundation (US)
- Subjects
Magnetic ordering ,Oscillations ,Thin films ,Spin-transfer-torque ,FOS: Physical sciences ,General Physics and Astronomy ,Spin wave ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,Oscil·lacions ,Oscillators ,Thin film ,Magnetic anisotropy ,Spin-½ ,Physics ,Pel·lícules fines ,Magnetisme ,Annihilation ,Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed matter physics ,Skyrmion ,Magnetism ,Anisotropia ,Microwave frequencies ,Vortex ,Nanocontacts ,Neuromorphic engineering ,Anisotropy ,Current (fluid) - Abstract
Magnetic droplet solitons are dynamical magnetic textures that form due to an attractive interaction between spin waves in thin films with perpendicular magnetic anisotropy. Spin currents and the spin torques associated with these currents enable their formation as they provide a means to excite non-equilibrium spin-wave populations and compensate their decay. Recent years have seen rapid advances in experiments that realize and study magnetic droplets. Important advances include the first direct x-ray images of droplets, determination of their threshold and sustaining currents, measurement of their generation and annihilation time, and evidence for drift instabilities, which can limit their lifetime. This perspective discusses these studies and contrasts these solitons to other types of spin-current excitations, such as spin-wave bullets, and static magnetic textures, including magnetic vortices and skyrmions. Magnetic droplet solitons can also serve as current controlled microwave frequency oscillators with potential applications in neuromorphic chips as nonlinear oscillators with memory., We thank our many collaborators over the years that have contributed to the experiments and ideas that have been discussed in this review: J. Albert, S. Bonetti, R. Kukreja, J. Hang, C. Hahn, J. M. Hernàndez, S. Lendínez, H. Ohldag, and N. Statuto. We thank Dan Stein for discussions and comments on this manuscript. Research at NYU related to neuromorphic computing was supported by Quantum Materials for Energy Efficient Neuromorphic Computing (Q-MEEN-C), an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), under No. Award DE-SC0019273. We also acknowledge fruitful discussions with Julie Grollier, Danijela Markovic, and Mark Stiles, which were initiated by Q-MEEN-C. F.M. acknowledges support from the Spanish Government through Grant Nos. RYC-2014-16515, MAT2015-69144-P, SEV-2015-0496, and MAT2017-85232-R. A.D.K. received support to conduct the x-ray microscopy and droplet lifetime experiments from the National Science Foundation under Grant No. DMR-1610416.
- Published
- 2020
22. Topology of the polarization field in PbTiO3 nanoparticles of different shapes by atomic-level simulations
- Author
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M. Sepliarsky, F. Di Rino, and M. G. Stachiotti
- Subjects
010302 applied physics ,Materials science ,Bubble ,General Physics and Astronomy ,02 engineering and technology ,purl.org/becyt/ford/1.3 [https] ,021001 nanoscience & nanotechnology ,Polarization (waves) ,Topology ,01 natural sciences ,Ellipsoid ,Ferroelectricity ,Toroidal moment ,Vortex ,purl.org/becyt/ford/1 [https] ,Molecular dynamics ,0103 physical sciences ,SPHERES ,0210 nano-technology - Abstract
An atomistic model approach parameterized from first-principles calculations is used to investigate size and shape effects on the polarization field in isolated stress-free PbTiO3 nanoparticles. The study was carried out by molecular dynamics simulations in free-standing nanodots of cylindrical, spherical, and ellipsoidal shapes. We show that in cylinders with diameter equal to height, the size-induced transformation from the vortex to the flux-closure domain configuration causes an anomaly in the behavior of the toroidal moment and the volume of the system. During this transformation, the vortex core evolves into domain walls while the resulting structure is stabilized due to the non-homogeneous distribution of polarization and strain inside the domains. A similar behavior is observed in elongated cylinders, spheres, and spheroids. The increment in the diameter/height relation of the nanoparticles gives rise to a succession of topological transformations that include multi-vortex configurations, ferroelectric bubble states, and multi-domain patterns. While the transformation path for flat cylinders is similar to the one previously obtained for cuboids, the thinner edge region of the spheroids prevents the stabilization of one- and two-bubble states. Despite this last difference, our results indicate that the polarization pattern of a nanoparticle depends more on its aspect ratio than on its shape. Fil: Di Rino, Franco Nicolas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentina Fil: Sepliarsky, Marcelo Claudio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentina Fil: Stachiotti, Marcelo Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentina
- Published
- 2020
23. Wave-induced vortex generation around a slender vertical cylinder
- Author
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Maurizio Brocchini, John Grue, Giulia Antolloni, Bjørn Hervold Riise, and Atle Jensen
- Subjects
Fluid Flow and Transfer Processes ,Physics ,Vortex tube ,Mechanical Engineering ,Computational Mechanics ,Breaking wave ,Mechanics ,Vorticity ,Condensed Matter Physics ,01 natural sciences ,010305 fluids & plasmas ,Vortex ,Physics::Fluid Dynamics ,Boundary layer ,Flow separation ,symbols.namesake ,Mechanics of Materials ,0103 physical sciences ,Froude number ,symbols ,Cylinder ,010306 general physics - Abstract
Experimental results of wave-induced vortex generation around a slender, vertical cylinder are discussed. Coherent vortices appear in long waves (kR ∼ 0.1, where k is the wave number and R is the cylinder radius) during the timing of the secondary load cycle, a strongly nonlinear component of the wave force acting on the cylinder, which is also measured. However, the secondary load cycle is also present in moderately long wave cases (kR ∼ 0.3) where there is no vortex formation. The measurement of vortex generation is enabled by particle image velocimetry. The flow downstream the cylinder, in three horizontal planes at different depths, is measured. The vortex formation that occurs in the long waves is attached to the cylinder in the form of thin vortex tubes. These appear symmetrically at angles of 40°–45° off the wave propagation direction. In one weak long wave case, several very thin vortex tubes appear along the back side of the cylinder. Vortex diameters are 20% of the cylinder diameter in four cases and 50% of the cylinder diameter in one case. The measured vorticity emanates from the cylinder’s boundary layer and is an order of magnitude stronger than the vorticity caused by wave breaking. Wave breaking reduces the vortex strength. The fact that the secondary load cycle appears without and with flow separation effects indicates that the load cycle is a gravity wave phenomenon that scales with the Froude number but that flow separation effects also contribute to the magnitude of such suction forces.
- Published
- 2020
24. Route to form skyrmions in soft magnetic films
- Abstract
Magnetic skyrmions which are topologically nontrivial magnetization configurations have attracted much attention recently due to their potential applications in information recording and signal processing. Conventionally, magnetic skyrmions are stabilized by chiral bulk or interfacial Dzyaloshinskii-Moriya interaction (DMI) in noncentrosymmetric B20 bulk crystals (at low temperatures) or ultrathin magnetic films with out-of-plane magnetic anisotropy (at room temperature), respectively. The skyrmion stability in the ultrathin films relies on a delicate balance of their material parameters that are hard to control experimentally. Here, we propose an alternate approach to stabilize a skyrmion in ferromagnetic media by modifying its surroundings in order to create strong dipolar fields of the radial symmetry. We demonstrate that artificial magnetic skyrmions can be stabilized even in a simple media such as a continuous soft ferromagnetic film, provided that it is coupled to a hard magnetic antidot matrix by exchange and dipolar interactions, without any DMI. Neel skyrmions, either isolated or arranged in a 2D array with a high packing density, can be stabilized using antidot as small as 40 nm in diameter for soft magnetic films made of Permalloy. When the antidot diameter is increased, the skyrmion configuration transforms into a curled one, becoming an intermediate between the Neel and Bloch skyrmions. In addition to skyrmions, the considered nanostructure supports the formation of nontopological magnetic solitons that may be regarded as skyrmions with a reversed core. (C) 2019 Author(s).
- Published
- 2019
25. Route to form skyrmions in soft magnetic films
- Abstract
Magnetic skyrmions which are topologically nontrivial magnetization configurations have attracted much attention recently due to their potential applications in information recording and signal processing. Conventionally, magnetic skyrmions are stabilized by chiral bulk or interfacial Dzyaloshinskii-Moriya interaction (DMI) in noncentrosymmetric B20 bulk crystals (at low temperatures) or ultrathin magnetic films with out-of-plane magnetic anisotropy (at room temperature), respectively. The skyrmion stability in the ultrathin films relies on a delicate balance of their material parameters that are hard to control experimentally. Here, we propose an alternate approach to stabilize a skyrmion in ferromagnetic media by modifying its surroundings in order to create strong dipolar fields of the radial symmetry. We demonstrate that artificial magnetic skyrmions can be stabilized even in a simple media such as a continuous soft ferromagnetic film, provided that it is coupled to a hard magnetic antidot matrix by exchange and dipolar interactions, without any DMI. Neel skyrmions, either isolated or arranged in a 2D array with a high packing density, can be stabilized using antidot as small as 40 nm in diameter for soft magnetic films made of Permalloy. When the antidot diameter is increased, the skyrmion configuration transforms into a curled one, becoming an intermediate between the Neel and Bloch skyrmions. In addition to skyrmions, the considered nanostructure supports the formation of nontopological magnetic solitons that may be regarded as skyrmions with a reversed core. (C) 2019 Author(s).
- Published
- 2019
26. Route to form skyrmions in soft magnetic films
- Abstract
Magnetic skyrmions which are topologically nontrivial magnetization configurations have attracted much attention recently due to their potential applications in information recording and signal processing. Conventionally, magnetic skyrmions are stabilized by chiral bulk or interfacial Dzyaloshinskii-Moriya interaction (DMI) in noncentrosymmetric B20 bulk crystals (at low temperatures) or ultrathin magnetic films with out-of-plane magnetic anisotropy (at room temperature), respectively. The skyrmion stability in the ultrathin films relies on a delicate balance of their material parameters that are hard to control experimentally. Here, we propose an alternate approach to stabilize a skyrmion in ferromagnetic media by modifying its surroundings in order to create strong dipolar fields of the radial symmetry. We demonstrate that artificial magnetic skyrmions can be stabilized even in a simple media such as a continuous soft ferromagnetic film, provided that it is coupled to a hard magnetic antidot matrix by exchange and dipolar interactions, without any DMI. Neel skyrmions, either isolated or arranged in a 2D array with a high packing density, can be stabilized using antidot as small as 40 nm in diameter for soft magnetic films made of Permalloy. When the antidot diameter is increased, the skyrmion configuration transforms into a curled one, becoming an intermediate between the Neel and Bloch skyrmions. In addition to skyrmions, the considered nanostructure supports the formation of nontopological magnetic solitons that may be regarded as skyrmions with a reversed core. (C) 2019 Author(s).
- Published
- 2019
27. Center Vortex Model for the Infrared Sector of SU(3) Yang-Mills Theory.
- Author
-
Quandt, Markus, Engelhardt, Michael, and Reinhardt, Hugo
- Subjects
- *
YANG-Mills theory , *SYMMETRY (Physics) , *PHASE transitions , *VORTEX motion , *INFRARED sources , *NUCLEAR models - Abstract
In this talk, we review some recent results of the center vortex model for the infrared sector of SU(3) Yang-Mills theory. Particular emphasis is put on the order of the finite-temperature deconfining phase transition and the geometrical structure of vortex branchings. We also present preliminary data for the ’t Hooft loop operator and the dual string tension near the phase transition. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]
- Published
- 2005
- Full Text
- View/download PDF
28. PIV of air flow over a step and discussion of fluctuation decompositions
- Author
-
Václav Uruba and Daniel Duda
- Subjects
Decomposition ,Materials science ,Velocity measurement ,Bubble ,Airflow ,Mechanics ,Air flow ,Particle image velocimetry ,Variations ,Vortex ,Physics::Fluid Dynamics ,Shear layer ,Aerodynamics ,Flow (mathematics) ,Fluid dynamics ,Fluid flow ,Layer (electronics) - Abstract
The experimental method of PIV (Particle image velocimetry) is used to study the air flow over a forward facing step creating shear layer between the outer flow and the recirculation bubble. This layer decays into vortices, which are highlighted by using Reynolds (temporal) decomposition or Agrawal (spatial) decomposition. The later can be tuned to different-sized structures, and, additionally, their energies roughly follow the Kolmogorov -5/3 law.
- Published
- 2018
29. Vortex motion in amorphous ferrimagnetic thin film elements
- Author
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Laura J. Heyderman, Eugenie Kirk, Harald Oezelt, Elisabeth Müller, Phillip Wohlhüter, Thomas Schrefl, and Alexander Kovacs
- Subjects
010302 applied physics ,Materials science ,Condensed matter physics ,Magnetic domain ,Physics ,General Physics and Astronomy ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,lcsh:QC1-999 ,Vortex ,Amorphous solid ,Core (optical fiber) ,Condensed Matter::Materials Science ,Magnetization ,Magnetic anisotropy ,Condensed Matter::Superconductivity ,0103 physical sciences ,ddc:530 ,0210 nano-technology ,Anisotropy ,Micromagnetics ,lcsh:Physics - Abstract
Amorphous Fe64Gd36 thin film square elements are investigated by imaging in theFresnel mode of a transmission electron microscope (TEM). The equilibrium statewithout an applied field shows the well-known four-domain flux closure patternwith in-plane magnetization. However, the vortex is displaced from the center ofthe square element and the domain walls are curved. In a reference measurement ofa thin Ni81Fe19 element, the vortex core is perfectly centered and the domain wallsstraight. When an increasing external field is applied in-plane, the vortex core canbe moved. While this motion of the vortex core is linear in NiFe elements, in theferrimagnetic FeGd squares the vortex core moves by sudden jumps. Micromagneticsimulations show that the asymmetry of the domain patterns as well as the vortexcore pinning and depinning can be attributed to random anisotropy and a patchymicrostructure in amorphous films., AIP Advances, 7 (5), ISSN:2158-3226
- Published
- 2017
30. Simulating marine propellers with vortex particle method
- Author
-
Wang, Youjiang, Abdel-Maksoud, Moustafa, and Song, Baowei
- Subjects
0209 industrial biotechnology ,Fast multipole method ,Computational Mechanics ,Ingenieurwissenschaften [620] ,02 engineering and technology ,01 natural sciences ,010305 fluids & plasmas ,020901 industrial engineering & automation ,0103 physical sciences ,Boundary element method ,Technik [600] ,Fluid Flow and Transfer Processes ,Physics ,Mechanical Engineering ,Skew ,Turbulence modeling ,Particle method ,Mechanics ,Condensed Matter Physics ,Boundary knot method ,Vortex ,Classical mechanics ,Mechanics of Materials ,ddc:620 ,Scale model ,ddc:600 - Abstract
The vortex particle method is applied to compute the open water characteristics of marine propellers. It is based on the large-eddy simulation technique, and the Smagorinsky-Lilly sub-grid scale model is implemented for the eddy viscosity. The vortex particle method is combined with the boundary element method, in the sense that the body is modelled with boundary elements and the slipstream is modelled with vortex particles. Rotational periodic boundaries are adopted, which leads to a cylindrical sector domain for the slipstream. The particle redistribution scheme and the fast multipole method are modified to consider the rotational periodic boundaries. Open water characteristics of three propellers with different skew angles are calculated with the proposed method. The results are compared with the ones obtained with boundary element method and experiments. It is found that the proposed method predicts the open water characteristics more accurately than the boundary element method, especially for high loading condition and high skew propeller. The influence of the Smagorinsky constant is also studied, which shows the results have a low sensitivity to it.
- Published
- 2017
31. Vortex identification from local properties of the vorticity field
- Author
-
Luca Moriconi and J. H. Elsas
- Subjects
Work (thermodynamics) ,Field (physics) ,Computational Mechanics ,FOS: Physical sciences ,Computational fluid dynamics ,Curvature ,01 natural sciences ,010305 fluids & plasmas ,Physics::Fluid Dynamics ,Linear filters ,Image processing ,Velocity gradient tensor ,0103 physical sciences ,Differential geometry ,Vortex dynamics ,Turbulent flows ,010306 general physics ,Fluid Flow and Transfer Processes ,Physics ,CIENCIAS EXATAS E DA TERRA::FISICA::AREAS CLASSICAS DE FENOMENOLOGIA E SUAS APLICACOES::DINAMICA DOS FLUIDOS [CNPQ] ,Turbulence ,Mechanical Engineering ,Mathematical analysis ,Fluid Dynamics (physics.flu-dyn) ,Monte Carlo methods ,Physics - Fluid Dynamics ,Vorticity ,Condensed Matter Physics ,Vortex ,Interpolation ,Identification (information) ,Mechanics of Materials ,Graph (abstract data type) ,Flow visualization - Abstract
It has been broadly acknowledged that vortex detection algorithms, usually based on linear-algebraic properties of the velocity gradient tensor, can be plagued with severe shortcomings and may become, in practical terms, dependent on the choice of subjective threshold parameters in their implementations. In two-dimensions, a large class of standard vortex identification prescriptions turn out to be equivalent to the "swirling strength criterion" ($\lambda_{ci}$-criterion), which is critically revisited in this work. We classify the instances where the accuracy of the $\lambda_{ci}$-criterion is affected by nonlinear superposition effects and propose an alternative vortex detection scheme based on the local curvature properties of the vorticity graph $(x,y,\omega)$ -- the "vorticity curvature criterion" ($\lambda_\omega$-criterion) -- which improves over the results obtained with the $\lambda_{ci}$-criterion in controlled Monte-Carlo tests. We show that the $\lambda_\omega$-criterion is able to cope with strong shear effects, if a subtraction of the mean velocity field background is performed, in the spirit of the Reynolds decomposition procedure. A realistic comparative study for vortex identification is then carried out for a direct numerical simulation (DNS) of a turbulent channel flow, including a three-dimensional extension of the $\lambda_\omega$-criterion. In contrast to the $\lambda_{ci}$-criterion, the $\lambda_\omega$-criterion indicates in a consistent way the existence of small scale isotropic turbulent fluctuations in the logarithmic layer, in consonance with long-standing assumptions commonly taken in turbulent boundary layer phenomenology., Comment: 20 pages, 23 figures
- Published
- 2017
32. Transient energy growth of optimal streaks in parallel round jets
- Author
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Pierre Brancher, J.I. Jiménez-González, Centre National de la Recherche Scientifique - CNRS (FRANCE), Institut National Polytechnique de Toulouse - INPT (FRANCE), Université Toulouse III - Paul Sabatier - UT3 (FRANCE), Universidad de Jaén - UJA (SPAIN), Institut de Mécanique des Fluides de Toulouse - IMFT (Toulouse, France), Universidad de Jaén (UJA), Institut de mécanique des fluides de Toulouse (IMFT), Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées, and Institut National Polytechnique de Toulouse - Toulouse INP (FRANCE)
- Subjects
Mécanique des fluides ,Computational Mechanics ,Perturbation (astronomy) ,02 engineering and technology ,Boundary layer thickness ,01 natural sciences ,010305 fluids & plasmas ,[SPI.MECA.MEFL]Engineering Sciences [physics]/Mechanics [physics.med-ph]/Fluids mechanics [physics.class-ph] ,Physics::Fluid Dynamics ,symbols.namesake ,0203 mechanical engineering ,0103 physical sciences ,Wavenumber ,Perturbation theory ,Navier–Stokes equations ,Optimal perturbation ,Fluid Flow and Transfer Processes ,Physics ,Mechanical Engineering ,Reynolds number ,Laminar flow ,Mechanics ,Condensed Matter Physics ,Vortex ,020303 mechanical engineering & transports ,Classical mechanics ,Mechanics of Materials ,symbols ,Jet flow ,Nonmodal stability analysis - Abstract
International audience; We present a linear optimal perturbation analysis of streamwise invariant disturbances evolving in parallel round jets. The potential for transient energy growth of perturbations with azimuthal wavenumber $m\geq1$ is analyzed for different values of Reynolds number Re. Two families of steady (frozen) and unsteady (diffusing) base flow velocity profiles have been used, for different aspect ratios $\alpha=R/\theta$, where $R$ is the jet radius and $\theta$ the shear layer momentum thickness. Optimal initial conditions correspond to infinitesimal streamwise vortices, which evolve transiently to produce axial velocity streaks, whose spatial structure and intensity depend on base flow and perturbation parameters. Their dynamics can be characterized by a maximum optimal value of the energy gain $G_{opt}$, reached at an optimal time $\tau_{opt}$ after which the perturbations eventually decays. Optimal energy gain and time are shown to be respectively proportional to Re^2 and Re, regardless of the frozen or diffusing nature of the base flow. Besides, it is found that the optimal gain scales like $G_{opt}\propto 1/m^3$ for all $m$ except $m=1$. This quantitative difference for azimuthal wavenumber $m=1$ is shown to be based on the nature of transient mechanisms. For $m = 1$ perturbations, the shift-up effect [J. I. Jiménez-González et al., “Modal and non-modal evolution of perturbations for parallel round jets,” Phys. Fluids 27, 044105-1–044105-19 (2015)] is active: an initial streamwise vorticity dipole induces a nearly uniform velocity flow in the jet core, which shifts the whole jet radially. By contrast, optimal perturbations with $m\geq2$, are concentrated along the shear layer, in a way that resembles the classical lift-up mechanism in wall-shear flows. The $m=1$ shift-up effect is more energetic than the $m\geq2$ lift-up, but it is slower, with optimal times considerably shorter in the case of $m\geq2$ disturbances. This suggests that these perturbations may emerge very quickly in the flow when injected as initial conditions. When the base flow diffuses, the large timescale for $m=1$ disturbances allows the shear layer to spread and the jet core velocity to decrease substantially, thus lowering the values of corresponding optimal gain and time. For $m\geq2$, results are less affected, since the shorter transient dynamics does not leave room for significant modifications of the base flow velocity profiles, and the scaling laws obtained in the frozen case are recovered. Nevertheless, base flow diffusion hinders the transient growth, as a consequence of a weaker component-wise non-normality and a smoother, radially spread structure of optimal disturbances.
- Published
- 2017
33. Magnetic field dependence of the internal quality factor and noise performance of lumped-element kinetic inductance detectors
- Author
-
Peter K. Day, Amber Miller, Bradley R. Johnson, Jonas Zmuidzinas, Robin Cantor, Sean Bryan, Heather McCarrick, Philip Daniel Mauskopf, Maximilian H. Abitbol, Glenn Jones, and Daniel Flanigan
- Subjects
Physics - Instrumentation and Detectors ,Materials science ,Physics and Astronomy (miscellaneous) ,Kinetic inductance detectors ,chemistry.chemical_element ,FOS: Physical sciences ,02 engineering and technology ,01 natural sciences ,Noise (electronics) ,Superconductivity (cond-mat.supr-con) ,Condensed Matter::Materials Science ,Aluminium ,Condensed Matter::Superconductivity ,0103 physical sciences ,Thin film ,010306 general physics ,Instrumentation and Methods for Astrophysics (astro-ph.IM) ,Condensed matter physics ,Condensed Matter - Superconductivity ,Instrumentation and Detectors (physics.ins-det) ,021001 nanoscience & nanotechnology ,Vortex ,Magnetic field ,chemistry ,Q factor ,Electromagnetic shielding ,Astrophysics - Instrumentation and Methods for Astrophysics ,0210 nano-technology - Abstract
We present a technique for increasing the internal quality factor of kinetic inductance detectors (KIDs) by nulling ambient magnetic fields with a properly applied magnetic field. The KIDs used in this study are made from thin-film aluminum, they are mounted inside a light-tight package made from bulk aluminum, and they are operated near $150 \, \mathrm{mK}$. Since the thin-film aluminum has a slightly elevated critical temperature ($T_\mathrm{c} = 1.4 \, \mathrm{K}$), it therefore transitions before the package ($T_\mathrm{c} = 1.2 \, \mathrm{K}$), which also serves as a magnetic shield. On cooldown, ambient magnetic fields as small as approximately $30 \, \mathrm{\mu T}$ can produce vortices in the thin-film aluminum as it transitions because the bulk aluminum package has not yet transitioned and therefore is not yet shielding. These vortices become trapped inside the aluminum package below $1.2 \, \mathrm{K}$ and ultimately produce low internal quality factors in the thin-film superconducting resonators. We show that by controlling the strength of the magnetic field present when the thin film transitions, we can control the internal quality factor of the resonators. We also compare the noise performance with and without vortices present, and find no evidence for excess noise beyond the increase in amplifier noise, which is expected with increasing loss., Comment: 5 pages, 4 figures
- Published
- 2016
34. Evolution of turbulence and in-plane vortices in the near field flow behind multi-scale planar grids
- Author
-
P.-Å. Krogstad and Lian Gan
- Subjects
Fluid Flow and Transfer Processes ,Physics ,Flow visualization ,Turbulence ,Mechanical Engineering ,Computational Mechanics ,Near and far field ,Geometry ,Vorticity ,Condensed Matter Physics ,Grid ,01 natural sciences ,010305 fluids & plasmas ,Vortex ,Correlation function (statistical mechanics) ,Classical mechanics ,Particle image velocimetry ,Mechanics of Materials ,0103 physical sciences ,010306 general physics - Abstract
In this experimental work, we carry out detailed two-dimensional particle image velocimetry investigations for the near field wakes behind a conventional and two multi-scale planar grids, using stitched camera fields of view. Statistical independent measurements are conducted focusing on the first few mesh distances downstream of the grid. It is found that the multiple integral length scales originated from the grids loose their importance on the turbulence development after about three mesh distances downstream, much earlier than the distance where the turbulence becomes homogeneous. The largest eddy size, represented by the integral length scales, does not show clear differences in its growth rate among the three grids after an initial development of three times the largest grid size downstream. Nevertheless, when examining individual vortex behaviours using conditional averaging and filtering processes, clear differences are found. The grids are found to have different decay rates of peak vorticity and projected vortex strengths. Despite these differences, the in-plane vorticity correlation function reveals that the mean vortex shape of all the grids shows a universal near-Gaussian pattern which does not change much as the turbulence decays.
- Published
- 2016
35. Translation of waves along quantum vortex filaments in the low-temperature two-dimensional local induction approximation
- Author
-
Robert A. Van Gorder
- Subjects
Fluid Flow and Transfer Processes ,Physics ,Mechanical Engineering ,Computational Mechanics ,Rotation around a fixed axis ,Quantum vortex ,Condensed Matter Physics ,Rotation ,Vortex ,Superfluidity ,symbols.namesake ,Classical mechanics ,Mechanics of Materials ,Orientation (geometry) ,symbols ,Kelvin wave ,Stationary state - Abstract
In a recent paper, we give a study of the purely rotational motion of general stationary states in the two-dimensional local induction approximation (2D-LIA) governing superfluid turbulence in the low-temperature limit [B. Svistunov, "Superfluid turbulence in the low-temperature limit," Phys. Rev. B 52, 3647 (1995)]. Such results demonstrated that variety of stationary configurations are possible from vortex filaments exhibiting purely rotational motion in addition to commonly discussed configurations such as helical or planar states. However, the filaments (or, more properly, waves along these filaments) can also exhibit translational motion along the axis of orientation. In contrast to the study on vortex configurations for purely rotational stationary states, the present paper considers non-stationary states which exhibit a combination of rotation and translational motions. These solutions can essentially be described as waves or disturbances which ride along straight vortex filament lines. As expected from our previous work, there are a number of types of structures that can be obtained under the 2D-LIA. We focus on non-stationary states, as stationary states exhibiting translation will essentially take the form of solutions studied in [R. A. Van Gorder, "General rotating quantum vortex filaments in the low-temperature Svistunov model of the local induction approximation," Phys. Fluids 26, 065105 (2014)], with the difference being translation along the reference axis, so that qualitative appearance of the solution geometry will be the same (even if there are quantitative differences). We discuss a wide variety of general properties of these non-stationary solutions and derive cases in which they reduce to known stationary states. We obtain various routes to Kelvin waves along vortex filaments and demonstrate that if the phase and amplitude of a disturbance both propagate with the same wave speed, then Kelvin waves will result. We also consider the self-similar solutions to the model and demonstrate that these types of solutions can model vortex kinks that gradually smooth and radiate Kelvin waves as time increases. Such solutions qualitatively agree with what one might expect from post-reconnection events.
- Published
- 2016
36. Non-local dynamics governing the self-induced motion of a planar vortex filament
- Author
-
Robert A. Van Gorder
- Subjects
Fluid Flow and Transfer Processes ,Physics ,Spacetime ,Mechanical Engineering ,Computational Mechanics ,Condensed Matter Physics ,Integral equation ,Vortex ,Vortex ring ,Protein filament ,Nonlinear system ,Classical mechanics ,Singularity ,Planar ,Mechanics of Materials - Abstract
While the Hasimoto planar vortex filament is one of the few exact solutions to the local induction approximation (LIA) approximating the self-induced motion of a vortex filament, it is natural to wonder whether such a vortex filament solution would exist for the non-local Biot-Savart dynamics exactly governing the filament motion, and if so, whether the non-local effects would drastically modify the solution properties. Both helical vortex filaments and vortex rings are known to exist under both the LIA and non-local Biot-Savart dynamics; however, the planar filament is a bit more complicated. In the present paper, we demonstrate that a planar vortex filament solution does exist for the non-local Biot-Savart formulation, provided that a specific non-linear integral equation (governing the spatial structure of such a filament) has a non-trivial solution. By using the Poincaré-Lindstedt method, we are able to obtain an accurate analytical approximation to the solution of this integral equation under physically reasonable assumptions. To obtain these solutions, we approximate local effects near the singularity of the integral equation using the LIA and non-local effects using the Biot-Savart formulation. Mathematically, the results constitute an analytical solution to an interesting nonlinear singular integrodifferential equation in space and time variables. Physically, these results show that planar vortex filaments exist and maintain their forms under the non-local Biot-Savart formulation, as one would hope. Due to the regularization approach utilized, we are able to compare the structure of the planar filaments obtained under both LIA and Biot-Savart formulations in a rather straightforward manner, in order to determine the role of the non-locality on the structure of the planar filament.
- Published
- 2016
37. Vortex motion of dust particles due to non-conservative ion drag force in a plasma
- Author
-
Kil-Byoung Chai and Paul M. Bellan
- Subjects
Physics ,Dusty plasma ,Ambipolar diffusion ,Motion (geometry) ,Magnetic reconnection ,Mechanics ,Plasma ,Condensed Matter Physics ,01 natural sciences ,010305 fluids & plasmas ,Vortex ,Ion ,Classical mechanics ,Drag ,Physics::Plasma Physics ,0103 physical sciences ,Astrophysics::Solar and Stellar Astrophysics ,Astrophysics::Earth and Planetary Astrophysics ,010306 general physics - Abstract
Vortex motion of the dust in a dusty plasma is shown to result because non-parallelism of the ion density gradient and the gradient of the magnitude of the ion ambipolar velocity cause the ion drag force on dust grains to be non-conservative. Dust grain poloidal vortices consistent with the model predictions are experimentally observed, and the vortices change character with imposed changes in the ion temperature profile as predicted. For a certain ion temperature profile, two adjacent co-rotating poloidal vortices have a well-defined X-point analogous to the X-point in magnetic reconnection.
- Published
- 2016
38. Magnetic versus non-magnetic pinning of vortices in superconducting films: Role of effective penetration depth
- Author
-
J. L. Vicent, J. del Valle, Elvira M. Gonzalez, and Alicia Gomez
- Subjects
Superconductivity ,Range (particle radiation) ,Materials science ,Physics and Astronomy (miscellaneous) ,Condensed matter physics ,Física de materiales ,Demagnetizing field ,02 engineering and technology ,Dissipation ,021001 nanoscience & nanotechnology ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,01 natural sciences ,Magnetic dots ,Magnetic field ,Vortex ,Penetration length ,Condensed Matter::Superconductivity ,0103 physical sciences ,Física del estado sólido ,010306 general physics ,0210 nano-technology - Abstract
In order to compare magnetic and non-magnetic pinning, we have nanostructured two superconducting films with the regular arrays of pinning centers: Cu (non-magnetic) dots in one case and Py (magnetic) dots in the other. For low applied magnetic fields, when all the vortices are pinned in the artificial inclusions, the magnetic dots prove to be better pinning centers, as has been generally accepted. Unexpectedly, when the magnetic field is increased and interstitial vortices appear, the results are very different: we show how the stray field generated by the magnetic dots can produce an effective reduction of the penetration length. This results in strong consequences in the transport properties, which, depending on the dot separation, can lead to an enhancement or worsening of the transport characteristics. Therefore, the election of the magnetic or non-magnetic character of the pinning sites for an effective reduction of dissipation will depend on the range of the applied magnetic field. Published by AIP Publishing.
- Published
- 2016
39. Pre-switching bifurcation of a slender jet
- Author
-
Denisse Sciamarella, Guillermo Artana, and Pierre Audier
- Subjects
Flow visualization ,Vortex tube ,Ciencias Físicas ,Computational Mechanics ,01 natural sciences ,Instability ,010305 fluids & plasmas ,010309 optics ,purl.org/becyt/ford/1 [https] ,0103 physical sciences ,Plasma actuator ,Bifurcation ,Fluid Flow and Transfer Processes ,Physics ,Física de los Fluidos y Plasma ,BIFURCATION ,Mechanical Engineering ,Mechanics ,purl.org/becyt/ford/1.3 [https] ,Condensed Matter Physics ,Vortex ,Flow control (fluid) ,Classical mechanics ,Particle image velocimetry ,Mechanics of Materials ,JET ,CIENCIAS NATURALES Y EXACTAS - Abstract
In this work, we study the near-field of the jet flow exiting a slot-model with aspect ratio 7.5:1. The core of the slender jet separates into two streams which subsequently merge recomposing a single core jet. Axis switching occurs downstream following self-similarity rules. In order to unveil the 3D dynamics of this pre-switching bifurcation, stereo-PIV (Particle Image Velocimetry) measurements are performed and a phase-locking technique is implemented using surface dielectric barrier discharge plasma actuators. The device forces the flow with low-amplitude localized disturbances to produce a lock-on phenomenon. The symmetric modes of the Crow instability, developing between the counter-rotating vortex tubes formed at the slot exit, are found to account for the bifurcation process. Fil: Audier, Pierre Marcel Roger. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Ingeniería Mecánica. Laboratorio de Fluidodinámica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Sciamarella, Denisse. Université Paris Sud; Francia Fil: Artana, Guillermo Osvaldo. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Ingeniería Mecánica. Laboratorio de Fluidodinámica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina
- Published
- 2016
40. Tight focusing of higher orders Laguerre-Gaussian modes
- Author
-
Ilya Golub, Dmitry Savelyev, and Svetlana N. Khonina
- Subjects
Electromagnetic field ,Physics ,Linear polarization ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Laser ,Polarization (waves) ,01 natural sciences ,Computational physics ,law.invention ,Vortex ,010309 optics ,law ,Electric field ,0103 physical sciences ,Laguerre polynomials ,Vector field ,0210 nano-technology - Abstract
The spatial redistribution of the contribution of different electric field components provides a decrease in the size of the central focal spot for higher orders Laguerre-Gaussian modes. It was shown that when sharply focusing laser beams with vortex or special binary phase plate, a sub-wavelength light localization of separate vector field components is possible for any polarization type. This fact should be considered for the interaction of laser radiation with materials selectively sensitive to lateral and longitudinal components of the electromagnetic field.
- Published
- 2016
41. Spectral enstrophy budget in a shear-less flow with turbulent/non-turbulent interface
- Author
-
G. Cocconi, Bettina Frohnapfel, Elisabetta De Angelis, Andrea Cimarelli, Cimarelli, A., Cocconi, G., Fronhapfel, B., and De Angelis, E.
- Subjects
Fluid Flow and Transfer Processes ,Physics ,Turbulent diffusion ,Computer simulation ,Turbulence ,Mechanical Engineering ,Computational Mechanics ,turbulence, interface, numerical simulation ,Condensed Matter Physics ,Enstrophy ,Vortex ,Physics::Fluid Dynamics ,Mechanics of Materials ,Cascade ,Inviscid flow ,Statistical physics ,TJ ,Anisotropy ,QC - Abstract
A numerical analysis of the interaction between decaying shear free turbulence and quiescent fluid is performed by means of global statistical budgets of enstrophy, both, at the single-point and two point levels. The single-point enstrophy budget allows us to recognize three physically relevant layers: a bulk turbulent region, an inhomogeneous turbulent layer, and an interfacial layer. Within these layers, enstro- phy is produced, transferred, and finally destroyed while leading to a propagation of the turbulent front. These processes do not only depend on the position in the flow field but are also strongly scale dependent. In order to tackle this multi-dimensional behaviour of enstrophy in the space of scales and in physical space, we analyse the spectral enstrophy budget equation. The picture consists of an inviscid spatial cascade of enstrophy from large to small scales parallel to the interface moving towards the interface. At the interface, this phenomenon breaks, leaving place to an anisotropic cascade where large scale structures exhibit only a cascade process normal to the interface thus reducing their thickness while retaining their lengths parallel to the interface. The observed behaviour could be relevant for both the theo- retical and the modelling approaches to flow with interacting turbulent/nonturbulent regions. The scale properties of the turbulent propagation mechanisms highlight that the inviscid turbulent transport is a large-scale phenomenon. On the contrary, the viscous diffusion, commonly associated with small scale mechanisms, highlights a much richer physics involving small lengths, normal to the interface, but at the same time large scales, parallel to the interface.
- Published
- 2015
42. Mixing and scalar dissipation rate statistics in a starting gas jet
- Author
-
N. Soulopoulos, Yannis Hardalupas, Alex M. K. P. Taylor, and Engineering & Physical Science Research Council (EPSRC)
- Subjects
Length scale ,Technology ,Fluids & Plasmas ,Scalar (mathematics) ,TURBULENT ,Computational Mechanics ,Mechanics ,09 Engineering ,AUTOIGNITION ,ENTRAINMENT ,PASSIVE SCALAR ,Physics, Fluids & Plasmas ,Statistics ,01 Mathematical Sciences ,Fluid Flow and Transfer Processes ,Physics ,Jet (fluid) ,Science & Technology ,02 Physical Sciences ,Mechanical Engineering ,NUMERICAL SIMULATIONS ,JOINT STATISTICS ,Dissipation ,Condensed Matter Physics ,Vortex ,Vortex ring ,MODEL ,Mechanics of Materials ,Planar laser-induced fluorescence ,Log-normal distribution ,Physical Sciences - Abstract
We quantify the temporal development of the mixing field of a starting jet by measuring the mixture fraction and the scalar dissipation rate and their statistics in an isothermal, impulsively started, gaseous jet. The scalar measurements are performed using planar laser induced fluorescence and, with appropriate processing of the resulting images, allow scalar dissipation rate measurements within 20%. The probability density functions of the mixture fraction, measured within a region of the order of 3 times the Batchelor length scale of the flow, are bimodal and skewed around a well-mixed radial location, which depends on the downstream distance and the time after the start of injection. The instantaneous distributions of the scalar dissipation rate reveal regions of high mixing at the jet periphery and at the developing vortex ring. The normalised probability density function (pdf) of the scalar dissipation rate at various flow positions and times after the start of injection has the same characteristic shape but differs from the usually suggested lognormal distribution at both low and high dissipation values; the same, also, holds true for the pdf conditioned on different values of the mixture fraction. The mean of the scalar dissipation rate conditional on mixture fraction shows a variation across the mixture fraction range, which differs between flow locations and times after the start of injection; however, at later times and for larger downstream distances the conditional mean between flow locations has similar distributions. Implications of the measurements for the auto-ignition of gaseous jets are examined and demonstrate that near the nozzle exit or at earlier times conditions are un-favourable for auto-ignition.
- Published
- 2015
43. A model for vortical plumes in rotating convection
- Author
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Rpj Rudie Kunnen, van Gjf Gert-Jan Heijst, J Jaap Molenaar, Jacobus W. Portegies, Mathematics and Computer Science, and Fluids and Flows
- Subjects
Convection ,cylinder ,Inertial frame of reference ,Computational Mechanics ,rayleigh-benard convection ,Rotation ,linear-theory ,Wiskundige en Statistische Methoden - Biometris ,fluid layer ,Rossby number ,Physics::Fluid Dynamics ,Geophysical fluid dynamics ,nonlinear convection ,Condensed Matter::Superconductivity ,motion ,greenland sea ,prandtl number ,Mathematical and Statistical Methods - Biometris ,Physics::Atmospheric and Oceanic Physics ,Rayleigh–Bénard convection ,Fluid Flow and Transfer Processes ,Physics ,Mechanical Engineering ,Mechanics ,Vorticity ,Condensed Matter Physics ,PE&RC ,Vortex ,Classical mechanics ,Mechanics of Materials - Abstract
Buoyant convection and the Coriolis force caused by the rotation of our Earth are important forces in the flows in the atmosphere and the oceans. A convenient model for such flows, although not fully compatible, is the rotating Rayleigh‐Benard setting: A horizontally infinite layer of fluid is vertically confined by solid walls rotating around a vertical axis, the bottom wall being at a higher temperature than the top wall. Although the lack of a top wall in the geophysical flows makes the model not directly applicable, the general behavior of the model flow shows considerable similarities to real flow in the atmosphere. Furthermore, in the atmosphere the tropopause can be regarded as a “top wall” to a certain extent. Especially for the large-scale flows in the atmosphere, the effect of the rotation is dominant. The Rossby number, the ratio between inertial and Coriolis forces, is rather small O0.1. A well-known theorem valid in rotation-dominated flows was formulated by Proudman 1 and experimentally proven by Taylor; 2 it is known as the Taylor‐Proudman theo
- Published
- 2008
44. On the large-scale structure and spectral dynamics of two-dimensional turbulence in a periodic channel
- Author
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Hjh Herman Clercx, W Werner Kramer, van Gjf Gert-Jan Heijst, Fluids and Flows, and Transport in Turbulent Flows (Clercx)
- Subjects
Computational Mechanics ,Flow simulation ,Enstrophy ,01 natural sciences ,010305 fluids & plasmas ,Physics::Fluid Dynamics ,symbols.namesake ,0103 physical sciences ,010306 general physics ,PACS-47.27.nd ,Channel flow ,Pressure gradient ,PACS-47.32.Ef ,PACS-47.27.nb ,Fluid Flow and Transfer Processes ,Physics ,Turbulence ,PACS-47.11.Kb ,Mechanical Engineering ,IR-62706 ,Boundary layer turbulence ,Reynolds number ,Mechanics ,Vortices ,Vorticity ,Condensed Matter Physics ,Vortex ,Open-channel flow ,PACS-47.32.cb ,Classical mechanics ,Flow (mathematics) ,Mechanics of Materials ,symbols ,PACS-47.60.Dx ,Numerical analysis - Abstract
This paper reports on a numerical study of forced two-dimensional turbulence in a periodic channel with flat no-slip walls. Since corners or curved domain boundaries, which are met in the standard rectangular, square, or circular geometries, are absent in this geometry, the (statistical) analysis of the flow is substantially simplified. Moreover, the use of a standard Fourier–Chebyshev pseudospectral algorithm enables high integral-scale Reynolds number simulations. The paper focuses on (i) the influence of the aspect ratio of the channel and (ii) the integral-scale Reynolds number on the large-scale self-organization of the flow. It is shown that for small aspect ratios, a unidirectional flow spontaneously emerges, notably in the absence of a pressure gradient in the longitudinal direction. For larger aspect ratios, the flow tends to organize into an array of counter-rotating vortical structures. The computed energy and enstrophy spectra provide further evidence that the injection of small-scale vorticity at the no-slip walls modify the inertial-range scaling. Additionally, the quasistationary final state of decaying turbulence is interpreted in terms of the Stokes modes of a viscous channel flow. Finally, the transport of a passive tracer material is studied with emphasis on the role of the large-scale flow on the dispersion and the spectral properties of the tracer variance in the presence of no-slip boundaries.
- Published
- 2008
45. Vortex states near the peak effect regime detected by voltage noise
- Author
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K. Kashiro, Satoshi Okuma, and N. Kokubo
- Subjects
Materials science ,Field (physics) ,Condensed matter physics ,Phase (matter) ,Condensed Matter::Superconductivity ,Phase diagram, Noise, Vortex Flow, Quantum Fluctuations ,Voltage noise ,Electric potential ,Edge (geometry) ,Vortex ,Magnetic field ,Amorphous solid - Abstract
We study the static and dynamic properties of vortices in the vortex solid phase of a thick amorphous MoxGe1−x film with Corbino‐disk (CD) and strip‐like contact geometries. For the strip‐like geometry the peak effect (PE) of the critical current Ic with magnetic field is clearly visible for all the temperatures studied and large voltage noise originating from current‐driven vortices appears in the field region just prior to a peak field where Ic takes a peak. For the CD geometry we observe essentially the same phenomena, indicating that the edge effects are not important for the static or dynamic properties of vortices.
- Published
- 2007
46. Effect of bubble’s arrangement on the viscous torque in bubbly Taylor- Couette flow
- Author
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G. Ndongo Fokoua, Céline Gabillet, Catherine Colin, Adrien Aubert, Institut de Recherche de l'Ecole Navale (IRENAV), Université de Bordeaux (UB)-Institut Polytechnique de Bordeaux-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Arts et Métiers Sciences et Technologies, HESAM Université (HESAM)-HESAM Université (HESAM), Institut de mécanique des fluides de Toulouse (IMFT), Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées, ANR-12-ASTR-0017 F-DRAIHN, Centre National de la Recherche Scientifique - CNRS (FRANCE), Ecole Navale (FRANCE), Institut National Polytechnique de Toulouse - Toulouse INP (FRANCE), Université Toulouse III - Paul Sabatier - UT3 (FRANCE), and Institut National Polytechnique de Toulouse - INPT (FRANCE)
- Subjects
Flow visualization ,Buoyancy ,Mécanique des fluides ,Taylor–Couette flow ,Computational Mechanics ,engineering.material ,01 natural sciences ,[SPI.MECA.MEFL]Engineering Sciences [physics]/Mechanics [physics.med-ph]/Fluids mechanics [physics.class-ph] ,010305 fluids & plasmas ,Physics::Fluid Dynamics ,Wall shear stress ,symbols.namesake ,viscous torque ,Bubbly flow ,Drag reduction ,0103 physical sciences ,Cylinder ,010306 general physics ,bubble dispersion ,Fluid Flow and Transfer Processes ,Physics ,Taylor Couette Flow ,Mechanical Engineering ,Reynolds number ,Taylor vortices ,Mechanics ,Bubble turbulence interaction ,Condensed Matter Physics ,Vortex ,Mechanics of Materials ,Drag ,symbols ,engineering ,Two-phase flow ,Mécanique: Mécanique des fluides [Sciences de l'ingénieur] - Abstract
An experimental investigation of the interactions between bubbles, coherent motion, and viscous drag in a Taylor-Couette flow with the outer cylinder at rest is presented. The cylinder radii ratio η is 0.91. Bubbles are injected inside the gap through a needle at the bottom of the apparatus. Different bubbles sizes are investigated (ratio between the bubble diameter and the gap width ranges from 0.05 to 0.125) for very small void fraction (α ≤ 0.23%). Different flow regimes are studied corresponding to Reynolds number Re based on the gap width and velocity of the inner cylinder, ranging from 6 × 102 to 2 × 104. Regarding these Re values, Taylor vortices are persistent leading to an axial periodicity of the flow. A detailed characterization of the vortices is performed for the single-phase flow. The experiment also develops bubbles tracking in a meridian plane and viscous torque of the inner cylinder measurements. The findings of this study show evidence of the link between bubbles localisation, Taylor vortices, and viscous torque modifications. We also highlight two regimes of viscous torque modification and various types of bubbles arrangements, depending on their size and on the Reynolds number. Bubbles can have a sliding and wavering motion near the inner cylinder and be either captured by the Taylor vortices or by the outflow areas near the inner cylinder. For small buoyancy effect, bubbles are trapped, leading to an increase of the viscous torque. When buoyancy induced bubbles motion is increased by comparison to the coherent motion of the liquid, a decrease in the viscous torque is rather observed. The type of bubble arrangement is parameterized by the two dimensionless parameters C and H introduced by Climent et al. [“Preferential accumulation of bubbles in Couette-Taylor flow patterns,” Phys. Fluids 19, 083301 (2007)]. Phase diagrams summarizing the various types of bubbles arrangements, viscous torque modifications, and axial wavelength evolution are built.
- Published
- 2015
47. Interaction between a laminar starting immersed micro-jet and a parallel wall
- Author
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Guillermo Artana, Cecilia Laborde, and J.M. Cabaleiro
- Subjects
Fluid Flow and Transfer Processes ,Flow visualization ,Physics ,Ingeniería Mecánica ,Jet (fluid) ,Mechanical Engineering ,Flow (psychology) ,Computational Mechanics ,Laminar flow ,LATERAL CONFINEMENT ,Mechanics ,TRANSIENT ,INGENIERÍAS Y TECNOLOGÍAS ,Condensed Matter Physics ,Vortex ,MICROJET ,Classical mechanics ,purl.org/becyt/ford/2 [https] ,LAMINAR ,Mechanics of Materials ,Position (vector) ,purl.org/becyt/ford/2.3 [https] ,Head (vessel) ,Scaling - Abstract
In the present work, we study the starting transient of an immersed micro-jet in close vicinity to a solid wall parallel to its axis. The experiments concern laminar jets (Re < 200) issuing from a 100 μm internal tip diameter glass micro-pipette. The effect of the confinement was studied placing the micro-pipette at different distances from the wall. The characterization of the jet was carried out by visualizations on which the morphology of the vortex head and trajectories was analyzed. Numerical simulations were used as a complementary tool for the analysis. The jet remains stable for very long distances away from the tip allowing for a similarity analysis. The self-similar behavior of the starting jet has been studied in terms of the frontline position with time. A symmetric and a wall dominated regime could be identified. The starting jet in the wall type regime, and in the symmetric regime as well, develops a self-similar behavior that has a relative rapid loss of memory of the preceding condition of the flow. Scaling for both regimes are those that correspond to viscous dominated flows. Fil: Cabaleiro, Juan Martin. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Ingeniería Mecánica. Laboratorio de Fluidodinámica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de la Marina Mercante. Facultad de Ingeniería. Laboratorio de Microfluidica y Plasmas; Argentina Fil: Laborde, Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Fisiología, Biología Molecular y Neurociencias. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Fisiología, Biología Molecular y Neurociencias; Argentina Fil: Artana, Guillermo Osvaldo. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Ingeniería Mecánica. Laboratorio de Fluidodinámica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina
- Published
- 2015
48. Interaction of dipolar vortices with a step-like topography
- Author
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G. J. F. van Heijst, L. Zavala Sansón, M. Tenreiro, and Fluids and Flows
- Subjects
Fluid Flow and Transfer Processes ,Physics ,Mechanical Engineering ,Computational Mechanics ,Tourbillon ,Mechanics ,Vorticity ,Condensed Matter Physics ,Rotating tank ,Vortex ,Dipole ,Classical mechanics ,Mechanics of Materials ,Inviscid flow ,Potential vorticity ,Barotropic fluid ,Physics::Atmospheric and Oceanic Physics - Abstract
The interaction of a barotropic, dipolar vortex with a step-like topography is studied by means of laboratory experiments in a rotating tank and by numerical simulations based on a quasi-two-dimensional model. Two main configurations are analyzed: when the dipole approaches a “low” or a “high” step with respect to the maximum water depth. For relatively low steps, the vortex crosses the topography with a deflected trajectory, while maintaining its dipolar structure. The sense of this deflection depends on whether the dipole reaches a step-up or a step-down. For high steps, in contrast, the dipole is not able to cross the topography, and the reflection of one of the dipole structures is observed. In both cases, one observes a weak flow along the topography with shallow water on its right. The essential features of the flow evolution for low and high steps can be explained by using arguments of potential vorticity conservation due to the weakness of viscous effects. In order to determine whether a barotropic dipole is able to cross the step or is reflected, qualitative criteria based on the step height and dipole strength are derived using inviscid arguments. © 2006 American Institute of Physics. DOI: 10.1063/1.2204070
- Published
- 2006
49. Symmetry breaking and vortex precession in low-swirling annular jets
- Author
-
E. Van den Bulck, Maarten Vanierschot, K. Van Dyck, and Paul Sas
- Subjects
Fluid Flow and Transfer Processes ,Convection ,Physics ,Jet (fluid) ,Turbulence ,Mechanical Engineering ,Computational Mechanics ,Reynolds number ,Mechanics ,Wake ,Condensed Matter Physics ,Stagnation point ,Vortex ,Physics::Fluid Dynamics ,symbols.namesake ,Mechanics of Materials ,Precession ,symbols - Abstract
© 2014 AIP Publishing LLC. In this paper, the flow dynamics in the wake of a turbulent annular jet is studied using Time-Resolved Stereoscopic Particle Image Velocimetry and Proper Orthogonal Decomposition (POD). In this wake, a central recirculation zone is present which, under certain conditions, shows a low-frequency precessing motion. POD analysis of the measured velocity data shows that at zero swirl, an asymmetry is present in the wake, which motion is random in time. This asymmetry originates from a bifurcation of the flow once a threshold Reynolds number is exceeded. For low-swirl numbers, ranging from 0 < S < 0.12, the asymmetry is still present and its motion becomes structured into a well defined precession. For S > 0.12, the precession is gone and the motion of the asymmetric wake is again random in time, similar like the non-swirling jet. In this paper, a model is developed to describe the influence of swirl on the wake dynamics. The model assumes that perturbations in the inner shear layer near the bluff body wall are convected towards the stagnation point. These perturbations cause a shift in the stagnation points position. This shift is convected back to the inner shear layer through convection in the recirculating flow. The dynamics of this feedback mechanism can be modeled by the nonlinear delayed saturation model. In this paper, the model is adapted for swirling flow and simulations show that good agreement is found with the experiments. ispartof: Physics of Fluids vol:26 issue:10 status: published
- Published
- 2014
50. The superfluid vortex cooler
- Author
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U Lindemann, de Atam Fons Waele, I Irina Tanaeva, N Jiang, and G Thummes
- Subjects
Superfluidity ,Physics ,Gravity (chemistry) ,Condensed matter physics ,Refrigerator car ,Base (geometry) ,General Physics and Astronomy ,Refrigeration ,Mechanics ,Cryogenics ,Superfluid helium-4 ,Vortex - Abstract
In this contribution a superfluid vortex cooler (SVC) is described. A SVC is a cooling device, the operation of which is based on the special properties of superfluid helium (He II). The SVC is small, simple, has no moving parts, and is gravity independent. It is capable of reaching temperatures as low as 0.65 K. First we have carried out a number of experiments, using a liquid-helium bath as a precooler for the SVC. Various geometries of the cooler components as well as the influence of the working pressure and the base temperature on the performance of the cooler have been investigated. Temperature below 1 K have been reached with a base temperature of 1.4 K. The next step has been combining the SVC with a pulse-tube refrigerator. In a preliminary experiment a lowest temperature of 1.19 K has been reached. Several ways to improve the system are suggested.
- Published
- 2005
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