Kinds Of Vortices Research Articles

0611 平板前縁から発生する空力音の多孔質材による低減効果(OS6 流体関連振動・騒音,オーガナイズドセッション)

Porous material is effective in reducing aerodynamic sound by changing properties of the surface of the object.It is considered that the porous material reduces two kinds of vortex causing aerodynamic sound.One is generated by the collision of turbulent flow to the object and the other is by the flow separation.In this study,the former is investigated by numerical simulation.A flat plate is adopted to avoid the flow separation.In our porous material model,inertial resistance is tuned to realize the flow field obtained in the previous experiment.We obtained reduced turbulence in front of the flat plate due to the porous material.

Rapid multivortex mixing in an alternately formed contraction-expansion array microchannel

We report a contraction-expansion array (CEA) microchannel for rapidly and homogeneously mixing different types of fluids by multivortex induced in alternately formed rectangular structures of the channel. Rapid mixing can be achieved in a topologically simple and easily fabricated CEA microchannel, employing a synergetic combination of two kinds of vortices: (1) expansion-vortices being induced by flow separation due to an abrupt change of cross-sectional area of the channel in its expansion region, and (2) Dean-vortices being induced by centrifugal forces acting on a cornering fluid through the channel. We experimentally and numerically investigated expansion- and Dean-vortices, and demonstrated rapid mixing of an aqueous solution containing fluorescein or human red blood cells (RBCs) at different flow rates corresponding to Reynolds number (Re) ranging from 7.2 to 43.0. Over 90% mixing efficiency at a channel length of 14.4 and 19.5mm was achieved at Re ≥ 28.6 (fluorescein solution and deionized water) and Re ≥ 21.5 (RBC suspension and phosphate buffered saline), respectively. The proposed CEA channel is expected to be useful for a wide range of applications where particles, cells and reagents must be rapidly and homogeneously mixed in microchannels.

Bose–Einstein Condensates with Non-classical Vortex

Coupled systems of nonlinear Schrodinger equations have been used extensively to describe Bose–Einstein condensates. In this paper, we study a two-component Bose–Einstein condensate (BEC) with an external driving field in a three-dimensional space. This model gives rise to a new kind of vortex–filaments, with fractional degree and nontrivial core structure. We show that vortex–filaments is 1-rectifiable set, and calculate its mean curvature in the strong coupling (Thomas–Fermi) limit. In particular, we show that large strength of the external driving field causes vortex–filaments for a two-component BEC.

Vortex pinning in two-gap superconductors

We discuss vortices and their pinning in two-gap superconductors, in which two superconducting gaps are opened around two different Fermi surfaces. We found that there are two kinds of vortices with continuously valuable fractions of the unit flux quanta hc/2e. These two kinds of vortices are tightly bound and cannot be separated in the ground state, but can be when deconfinement occurs by the finite temperature effect as is pointed out (See, Jun Goryo, Shingo Soma, and Hiroshi Matsukawa, Europhys. Lett. 80 (2007) 17002). In this paper, we show that two kinds of vortices can be split by the pinning effect.

Magneto-optical imaging of vortex lensing in Bi 2Sr 2CaCu 2O 8+ y

In a highly anisotropic superconductor Bi 2Sr 2CaCu 2O 8+ y , crossing-lattices state of pancake and Josephson vortices is realized under tilted magnetic fields. In this state, one kind of vortices can drag another, opening a possibility to control the arrangements and motion of vortices in a novel way. We have demonstrated the focusing of pancake vortices in the center of the sample, vortex lensing, by differential magneto-optical imaging in Bi 2Sr 2CaCu 2O 8+ y . The final arrangement of vortices changes depending on the ramping rate of the in-plane field. Such a behavior is discussed in relation with the competition between the drag force by Josephson vortices and the vortex dome formation due to the surface barrier.

The crossing-lattices state in Bi2Sr2CaCu2O8+y

In the highly anisotropic superconductorBi2Sr2CaCu2O8+y, two kinds of vortices, pancake vortices (PVs) and Josephson vortices (JVs), coexist undertilted magnetic fields and form a novel ground state of vortex matter. Such a state is calledthe crossing-lattices state, where attractive interactions between PVs and JVslead to various arrangements of vortices. We demonstrate the complicated phasediagram of the crossing-lattices state by means of micro-Hall probe magnetometry,magneto-optical observations, and Bitter decoration technique. The attractive interactionsbetween PVs and JVs is also utilized to control the motion of PVs using JVs.

Velocity field vortices and Mermin-Ho vortices in two-component spinor BEC

In light of the φ-mapping topological current theory, two important vortex structures in two-component spinor BEC—the velocity field vortices and the Mermin-Ho vortices are discussed. It is revealed that these two different kinds of vortices are created respectively from the zero points of two different order parameter configurations in the condensates, and both their topological charges, locations and motions can be determined by the φ-mapping theory.

Coherent structures in countercurrent axisymmetric shear flows

The dynamical behaviors of coherent structures in countercurrent axisymmetric shear flows are experimentally studied. The forward velocityU1 and the velocity rationR=(U1-U2)/(U1+U2), whereU2 denotes the suction velocity, are considered as the control parameters. Two kinds of vortex structures, i.e., axisymmetric and helical structures, were discovered with respect to different regimes in theR versusU1 diagram. In the case ofU1 ranging from 3 to 20m/s andR from 1 to 3, the axisymmetric structures play an important role. Based on the dynamical behaviors of axisymmetric structures, a critical forward velocityU1cr=6.8m/s was defined, subsequently, the subcritical velocity regime:U1>U1cr and the supercritical velocity regime:U1 4m/s), correspondingly, the spatial evolution of the temporal asymptotic behavior of a dynamical system can be described as follows: (1) Hopf bifurcation, (2) subharmonic bifurcation, (3) reversed superharmonic bifurcation, (4) superharmonic bifurcation, (5) chaos (“weak turbulence”) in the case ofU1 4m/s). The proposed new terms, superharmonic and reversed superharmonic bifurcations, are characterized of the frequency doubling rather than the period doubling. A kind of unfamiliar vortices referred to as the helical structure was discovered experimentally when the forward velocity around 2m/s and the velocity range from 1.1 to 2.3. There are two base frequencies contained in the flow system and they could coexist as indicated by the Wigner-Ville-Distribution and the temporal asymptotic behavior of the dynamical system corresponding to the helical vortex could be described as 2-torus as indicted by the 3D reconstructed phase trajectory and correlation dimension. The scenario of the spatial evolution of helical structures could be described as follows: the jet column is separated into two parts at a certain spatial location and they entangle each other to form the helical vortex until the occurrence of those separated jet columns to reconnect further downstream with the result that the flow system evolves into turbulence in a catastrophic form. Correspondingly, the dynamical system evolves directly into 2-torus through the supercritical Hopf bifurcation followed by a transition from a quasi-periodic attractor to a strange attractor. In the case ofU1=2m/s, the parametric evolution of the temporal asymptotic behavior of the dynamical system as the velocity ratio increases from 1 to 3 could be described as follows: (1) 2-torus (Hopf bifurcation), (2) limit cycle (reversed Hopf bifurcation), (3) strange attractor (subharmonic bifurcation).

Electron vortexes in high-current plasma lens

High-current plasma lens (PL) instability of two-dimensional oscillations caused by unremovable radial gradients of the magnetic field and fast ion beams are considered. It is supposed that electron motion is nonlinear and ion motion is linear. The nonlinear differential equation of the electric potential in a hydrodynamical approximation is obtained and its solutions are found for different configurations of external magnetic fields. It is shown that these solutions may be represented in the form of stable vortex structures. Computer models for such kinds of vortices have been created. Creation of vortexes limits maximum values of space electrostatic fields in plasma optics. In the low current regime of the PL with strong ion beam space charge overcompensation, the equation obtained describes nonlinear motion of the electron fluid caused by diocotron instability.

SuperDARN‐detected plasma convection vortices and the global plasma convection

Routine Super Dual Auroral Radar Network (SuperDARN) ionospheric plasma convection maps were used to assess the performance of the Weimer 96 model, which predicts a convection pattern for the entire high‐latitude ionosphere for any value of the interplanetary magnetic field (IMF) By and Bz components, the solar wind speed, and the seasonal dipole tilt angle. Reasonable agreement between model predictions and SuperDARN measurements are shown for the most typical IMF orientations on the clock diagram and moderate IMF intensities between 1 nT and 5 nT. Global convection patterns were then derived for the periods when the SuperDARN HF radars detected mesoscale quasi‐stable convection vortices. The earlier finding that convection vortices with clockwise (CW) plasma circulation occur at the dayside ends of large‐scale dusk convection cells (for Bz < 0) was confirmed, but only for 9 events out of 25 events that were studied. We found that vortices can occur at the dayside ends of dawn convection cells. The sense of plasma circulation in these vortices is counterclockwise (CCW). We also found that CW and CCW convection vortices can occur, though rarely, at the night ends of large‐scale convection cells, dusk and dawn, respectively. We found that in 11 vortex events out of all events studied the SuperDARN maps were simply showing plasma circulation around the foci of the global convection cells (Bz > 0 and Bz < 0). For strongly northward IMF, there were located two vortex events for which vortices represented the entire cell in a multicell global plasma convection pattern. These results indicate that different mechanisms for vortex formation should be considered, depending on what kind of vortex has formed.

Studies on Reduction of Fluid Drag For Athelete Swimming Suit by Boundary Layer Control.

Sport science progresses step by step in the world. The paper describes, the first, the relationships between fluid drag for a model of woman swimmer and the flow around it. The flow around the model swimmer is very complicated, and includes, for example, wave, some kinds of vortices, hydraulic jumping and so on. The complicated flows are visualized by the surface tufts method and so on. Second, the possibility of the reduction of fluid drag for a woman athlete swimming suit is challenged. The boundary layer control is applied to reduce the fluid drag. The separation occurs around the breast of a woman swimmer. The separation can be suppressed by the boundary layer control. Many beads are distributed on the breast area of a woman swimming suit. As the result, it is found that the fluid drag for the model swimmer can be reduced in a range of 1.5%∼2% by the suit with the boundary layer control, which is carried out by many beads.

Phase coherence along the c-axis in Bi 2Sr 2CaCu 2O 8+ y with columnar defects probed by Josephson plasma resonance

We studied the c-axis phase coherence in Bi 2Sr 2CaCu 2O 8+ y with columnar defects using the Josephson plasma resonance as a probe. At temperatures close to T c, the Josephson plasma resonance field ( H p) shows a characteristic temperature dependence of decoupled pancake vortices similar to the pristine Bi 2Sr 2CaCu 2O 8+ y . The drastic increase in H p occurs at a frequency independent characteristic field even in the vortex liquid phase. We interpret this change as a manifestation of recoupling of decoupled vortices by the columnar defects. The increase in H p becomes larger with increasing the density of columnar defects. The temperature dependence of H p at lower temperatures but above the irreversibility line can be understood by considering two kinds of vortices, some trapped in the columnar defects and others located between them giving a decoupled liquid-like response.

Transition waves and nonlinear interactions in the near wake of a circular cylinder

Transition waves and interactions between two kinds of instability—vortex shedding and transition wave in the near wake of a circular cylinder in the Reynolds number range 3 000–10 000 are studied by a domain decomposition hybrid numerical method. Based on high resolution power spectral analyses for velocity new results on the Reynolds-number dependence of the transition wave frequency, i.e.f t /fs∼Re0.87 are obtained. The new predictions are in good agreement with the experimental results of Wei and Smith but different from Braza s prediction and some early experimental resultsf t/fs∼Re 0.5 given by Blooret al. The multi-interactions between two kinds of vortex are clearly visualized numerically. The strong nonlinear interactions between the two independent frequencies (f t,f s ) leading to spectra broadening to form the couplingmf s +nf t are predicted and analyzed numerically, and the characteristics of the transition are described. Longitudinal variations of the transition wave and its coupling are reported. Detailed mechanism of the flow transition in the near wake before occurrence of the thedimensional evolution is provided.

Nonlinear Equilibration of Two-Dimensional Eady Waves: A New Perspective

Abstract The equilibration of two-dimensional baroclinic waves differs fundamentally from equilibration in three dimensions because two-dimensional eddies cannot develop meridional temperature or velocity structure. It was shown in an earlier paper that frontogenesis together with diffusive mixing in a two-dimensional Eady wave brings positive potential vorticity (PV) anomalies deep into the atmosphere from both boundaries and allows the disturbance to settle into a steady state without meridional gradients. Here we depart from the earlier explanation of this equilibration and associate the PV intrusions with essentially the same kind of vortex “roll-up” that characterizes the evolution of barotropic shear layers. To avoid subgrid turbulence parameterizations and computational diffusion, the analogy is developed using Eady's generalized baroclinic instability problem. Eady's generalized model has two semi-infinite regions of large PV surrounding a layer of relatively small PV. Without boundaries, frontal ...

Expressions for pressure-velocity-gradient correlations

The term for pressure-velocity-gradient correlation was initiated by Rotta's[21] rewriting the correlation between the pressure fluctuation gradient and velocity fluctuation. However, it is very difficult to consider the effect of this term. Since Rotta's work, Launder et al.[7] has made some estimates of this term. In this paper according to the equations for velocity fluctuation, the pressure fluctuation is solved so that the average value of the product of the pressure fluctuation and the velocity fluctuation gradient is obtained. Thus, the whole expressions for the pressure-velocity-gradient correlation are derived. The result explains that the limited expressions by Rotta and Launder are reasonable to a certain degree. The whole expressions in this paper are discussed respectively in two situations: one is without a separate consideration of large and small vortexes; the other is with a separate consideration of three kinds of vortexes. Therefore, the paper gives the whole expressions for pressure-velocity-gradient correlation to the Reynolds stress turbulence model[7] and the three-vortex turbulence model[13].

Scattering of low-energy fermions by a Chern-Simons vortex.

We consider the interaction of (2+1)-dimensional fermions with a background of a charged-vortex solution of the Chern-Simons-Higgs model. When the fermions are coupled in the minimal way to the vortex gauge fields, the interaction potentials contain short-range terms, related to the vortex electric and magnetic field, and long-range terms, proportional to the topological charge of the vortex, that modify the centrifugal barrier. As a consequence of this inverse-square tail, at a large distance from the center of the vortex, the fermion behaves as if it had an effective angular momentum that, because of the difference between the fermion charge e and the scalar charge q, can assume any rational value. We develop a procedure to study the scattering of low-energy fermions by any kind of vortex and with a partial-wave analysis we compute, for any value of the fermion angular momentum, the phase shifts, the Jost functions, and the scattering cross sections. The obtained results crucially depend on the quantity en/q (n being the vorticity) and the low-energy cross section diverges at zero momentum.

Alfvén vortices and related phenomena in the ionosphere and the magnetosphere

Satellite (IC-B-1300) data on the electromagnetic structures in the high-latitude ionosphere are presented. One can observe three kinds of vortices, namely vortex chains as well as solitary dipolar and monopolar vortex structures. The theoretical treatment that is carried out in the present paper is in reasonable agreement with the observations.

The wake structures of two-dimensional rectangular cylinders having different length-to-width ratios. (The case of the angle of attack 0 deg.

The wake structures of two-dimensional rectangular cylinders with length-to-width ratios, l/h, ranging from 0.25 to 4.0 were experimentally investigated by means of the phase averaging technique. The vortex region of the wake remarkably extended at l/h = 2.0. There were two kinds of vortices in the region 2.0≤l/h<3.0. One was formed by the rolling shear layer separated from the leading edges of the cylinder, and the other was the vortex shedding from the rear edges which was also formed by the attached shear layer from the leading edges on the side walls of the cylinder. In case of l/h over 3.0, the vortex region became more narrow and the vortex strength more intense than at the small values of l/h.

On the multiple structure of atmospheric vortices

Various scales of the multiple‐vortex phenomena observed in atmospheric vortices are reviewed and summarized. The nonaxisymmetric feature clearly seen in small‐scale vortices such as tornadoes is also recognized in the vortices of tropical cyclones. On the basis of both the physical resemblances and the swirl ratio similarity, this asymmetry in tropical cyclones is concluded to be a manifestation of multiple vortices. It is suggested that the evolution of a vortex from one‐cell to two‐cell to multiple vortices is a common feature in nature found not only in tornadoes, but also in other kinds of vortices, ranging from dust devils to tropical cyclones.

Experiments with negative ions in rotating superfluid 3He–A

Ion-mobility experiments on rotating superfluid 3He–A show that the l-vector texture in the liquid strongly focuses ions to vortex cores and that two different kinds of vortices, with clearly different ion mobilities along their cores, exist in the A phase, depending on the preparation of the rotating state and on the external magnetic field.