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1.
A flow induced by a rotating disk mounted at the top of a cubic container totally filled with a liquid is studied experimentally.
The flow pattern is visualized for Reynolds numbers in the interval 1500–6000, and the velocity variation along the axis of
the container, which coincides with the axis of revolution of the disk, is observed by means of Doppler laser anemometry (DLA).
As Re grows, the velocity axial component starts fluctuating because of the vortex core precession. The breakdown of the vortex
helical structure becomes pronounced at Re>4000 without the formation of the return flow region (vortex breakdown bubble)
at the axis. With the Reynolds number and the container height-to-disk radius ratio being the same, the axial flow patterns
in standard cylindrical [1] and cubic containers differ radically. In the latter vessel at low Re, the steady flow regime
and axisymmetric bubble breakdown of the vortex structure near the axis are absent. 相似文献
2.
V. N. Buravtsev A. V. Nikolaev A. V. Ukrainets 《Moscow University Physics Bulletin》2009,64(4):442-445
The impact of platelet collisions on their distribution in a viscous liquid flow has been analyzed. It has been shown that
platelet distribution in the flow perpendicular to current lines resulting from their collisions can be described as “shear”
diffusion. In the wide physiological range of shear velocities specific for blood, the coefficient of “shear” diffusion is
much larger than the coefficient of “Brownian” diffusion. For a parabolic fluid velocity profile (Poiseuille flow) in cylindrical
vessel “shear” diffusion causes uneven radial distribution of platelets over the vessel radius. “Shear” diffusion causes platelet
concentration to grow from the wall toward the center (vessel axis). This effect appears to be a consequence of the specific
distribution of platelet collision frequency reaching its maximum at the vessel wall. 相似文献
3.
I. A. Bakunina G. Ya. Smolkov S. D. Snegirev 《Radiophysics and Quantum Electronics》2008,51(8):579-596
Two basic “geometric” effects manifest themselves as slow variations in the properties of the microwave radiation of the active
region passing through the solar disk, namely 1) sign inversions of the circular polarization and 2) characteristic peaks
of the brightness temperature at certain longitudes on both sides of the central solar meridian and depression near it. These
effects are related to the magnetic directivity of the cyclotron radiation governing in the centimeter wavelength range above
large spots. The concept of “normal” passage of the active region through the solar disk is introduced in this paper on the
basis of studying the mentioned effects observed at two wavelengths, 5.2 cm (Siberian Solar Radiotelescope, Buryatiya) and
1.76 cm (Radioheliograph in Nobeyama, Japan), to separate the “normal,” or “geometric” effects, in the behavior of the microwave
radiation from the evolutional effects that may cause high-power solar flares.
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 8, pp. 641–659, August 2008. 相似文献
4.
The subject of consideration is a uniformly charged jet of an ideal incompressible conducting liquid moving with a constant velocity along the symmetry axis of an undisturbed cylindrical surface. An evolutionary expression for the jet shape is derived accurate to the second order of smallness in oscillation amplitude for the case when the initial deformation of the equilibrium surface is a superposition of a finite number of both axisymmetric and nonaxisymmetric modes. The flow velocity field in the jet and the electric field distribution near it are determined. The positions of internal nonlinear secondary combined three-mode resonances are found, which are typical of nonlinear corrections to the analytical expressions for the jet shape, flow velocity field potentials, and electrostatic field in the vicinity of the jet. 相似文献
5.
Alexander I. Nosich Elena I. Smotrova Svetlana V. Boriskina Trevor M. Benson Phillip Sewell 《Optical and Quantum Electronics》2007,39(15):1253-1272
Research into microdisk lasers demonstrates new achievements both in the technology and in the associated physical effects
and applications. Melting and rounding of the disk edge boosts the Q-factors due to improved surface smoothness. In-plane
cavity shape is widely used as a design instrument. Optimal shaping of pumped area lowers the threshold power. Photonic molecules
made of several microdisks as “photonic atoms” show lasing at several closely spaced frequencies. A microdisk with a single
quantum dot as an active region is considered as the most promising system for realisation of a single photon emitter necessary
for quantum computing. These new effects and devices can be simulated with accurate numerical techniques, developed recently
for “warm-cavity” linear modelling, that are able to bring a new vision of the physics of lasing. 相似文献
6.
In situ morphological investigation of the “105” faceted Ge islands on the Si(001) surface (hut clusters) have been carried
out using an ultra high vacuum instrument integrating a high resolution scanning tunnelling microscope and a molecular beam
epitaxy vessel. Both species of hut clusters-pyramids and wedges-were found to have the same structure of the “105” facets
which was visualized. Structures of vertexes of the pyramidal clusters and ridges of the wedge-shaped clusters were revealed
as well and found to be different. This allowed us to propose a crystallographic model of the “105” facets as well as models
of the atomic structure of both species of the hut clusters. An inference is made that transitions between the cluster shapes
are impossible. 相似文献
7.
The flow pattern around a thin strip horizontally towed at constant velocity in a continuously stratified liquid is visualized
by conventional “Vertical slit-Foucault’s knife”, “Maksoutov’s slit-thread” and “horizontal slit-regular grating” methods.
Using these sensitive high-resolution methods enables to reveal new kind of the streaky structure including a sequence of
thin sloping interfaces both on the strip surface and inside its wake. When velocity or distance from the strip increases,
the streaks may be turned into the sloping or nearly horizontal interfaces. Reconnections of outer edges of the streaks result
in appearance of a set of symmetrical “butterfly-like” vortices, which are perturbed by a shear flow inside the downstream
wake. Lift forces caused by a slope of the strip produce an asymmetry of the wake and lead to fast degeneration ofthe streaky
structures. 相似文献
8.
Influence of radial electric field on trajectories of plug potential bounce ion in the tandem mirror
K. Ishii A. Fueki Y. Takemura A. Kojima H. Hagisawa I. Katanuma K. Yatsu 《Czechoslovak Journal of Physics》2002,52(10):1135-1142
Bouncing ions between the plug potentials play an important role in improvement of the axial confinement in the tandem mirror.
We examined the influence of the radial electric field on the trajectories of the ions passed through the anchor cell with
nonaxisymmetric magnetic configuration on the assumption that the shape of the magnetic flux tube was shifted from the shape
of the equipotential surface of the plasma at the mirror throats of the anchor cells. The discrepancy between the shapes enhanced
the radial drift of the bounce ion. Radial potential profile of the core plasma was controlled by adjustment of the radially
separated endplate potentials, and it was found that the flattened radial potential profile was effective for the decrease
of the radial drift.
Presented at 5th Workshop “Role of Electric Fields in Plasma Confinement and Exhaust”, Montreux, Switzerland, June 23–24,
2002. 相似文献
9.
Comparative analysis of aerodynamics of waveriders designed on the basis of conical and planar flows
I. I. Mazhul 《Thermophysics and Aeromechanics》2007,14(1):93-105
A comparative analysis of the aerogasdynamics of waveriders designed from two different flow types, namely the axisymmetric
conical flows and the flows behind two-dimensional planar shocks, was carried out. Integral aerodynamic characteristics of
a configuration with different forms of transverse contours of the lower surface were considered, and the “conical” and equivalent
“planar” waveriders optimal in terms of the life-todrag ratio were compared. The gas-dynamic structure features in off-design
flow regimes were investigated on the basis of numerical solution of the Euler equations for the Mach numbers, which were
both higher and lower than the design values. Obtained data refer to the freestream Mach number range M∞ = 4–10. 相似文献
10.
Bruce William Lites 《中国科学G辑(英文版)》2009,52(11):1660-1664
The Hinode mission has provided us with a new, quantitative view of the magnetism of the quiet Sun. It has revealed that the
quiet internetwork areas are blanketed by horizontal fields that appear at first sight to have more flux than the vertical
fields resolved on the same 0.3″ size scale. These measurements point to the possibility that the horizontal fields might
be the primary source of the “hidden turbulent flux” of the quiet Sun anticipated from Hanle effect depolarization. In this
paper, evidence is presented suggesting that the “seething” horizontal fields observed by Harvey in 2007 and the horizontal
fields revealed by Hinode are the same phenomenon. Because the seething fields appear to be of uniform fluctuation over the
whole disk, the phenomenon is most likely not associated with the dynamo source of solar activity. Thus, the small-scale “hidden
turbulent flux” lends support to the notion of a local solar dynamo acting on granular sizes and time scales. 相似文献
11.
Direct measurement of fluid velocity gradients at a wall by PIV image processing with stereo reconstruction 总被引:1,自引:0,他引:1
Velocity gradient is typically estimated in Particle Image Velocimetry (PIV) by differentiating a measured velocity field,
which amplifies noise in the measured velocities. If gradients near a boundary are sought, such noise is usually greater than
in bulk fluid, because of small tracer displacement, uncertainty in the effective positions of velocity vectors, intense deformation
of tracer patterns, and laser reflection. We consider here a modified form of the Particle Image Distortion (PID) method todirectly calculate velocity gradients at a fixed wall, and refer it as “PIV/IG” (“Interface Gradiometry”). Results from synthetic
2D PIV images suggest our method achieves higher SNR and accuracy than velocity differentiation. Also, we have developed a
procedure to reconstruct three-dimensional velocity gradient at a fixed wall the two non-zero components from PIV/IG data
obtained in stereo views; these equations simplify considerably thanks to the no-slip condition. Experimental data from the
bottom wall of turbulent open channel flow appear to suffer from a form of pixel locking. As with standard PIV, this underlines
the importance of adequate tracer diameter in the images, sufficient seeding density, and of dynamic range of the camera sensor. 相似文献
12.
In this work, we present a numerical study of the laminar-turbulence transition flow around a symmetrical air-foil at a low Reynolds number in free flow and near the ground surface at different angles of attack. Finite volume method is employed to solve the unsteady Reynolds-averaged Navier–Stokes (RANS) equation. In this way, the Transition SST turbulence model is used for modeling the flow turbulence. Flow around the symmetrical airfoil SD7003 is numerically simulated in free stream and near the ground surface. Our numerical method can detect different aspects of flow such as adverse pressure gradient, laminar separation bubble and laminar to turbulent transition onset and the numerical results are in good agreement with the experimental data. 相似文献
13.
The flow pattern around a horizontal cylinder towed at constant velocity along isopycnic plane in a continuously stratified
liquid is visualized by conventional techniques of “Vertical slit-Foucault’s knife”, “Maksoutov’s slit-thread” and “horizontal
slit-regular grating”. Using sensitive high-resolution methods allows detail studying such component of stratified flow structures
as soaring interfaces, singular soaring vortices and vortex systems, which arise directly inside the internal waves field
past the cylinder. These flow elements having high level of vorticity are separated from the downstream wake by a strip of
fluid without any small-scale inhomogeneities. Formation of singular vortex dipoles on leading edges of soaring interfaces
is investigated in details in a wide range of flow parameters. 相似文献
14.
15.
The shear layer evolution and turbulent structure of near-wake behind a sphere atRe= 11,000 and 5,300 were investigated using a smoke-wire visualization method. A laminar flow separation was found to occur
near the equator. The smooth laminar shear layers appeared to be axisymmetrically stable to the downstream location of aboutx/d=1.0 atRe=11,000 andx/d= 1.7∼1.8 atRe=5,300, respectively. At Re=11,000, the vortex ring-shaped protrusions were observed with the onset of shear layer instability.
Moreover, the transition from laminar to turbulence in the separated flow region occurred earlier at the hiher Reynolds number
ofRe=11,000 than atRe=5,300. The PIV measurements in the streamwise and cross-sectional planes atRe=11,000 clearly revealed the turbulent structures of the sphere wake such as recirculating flow, shear layer instability,
vortex roll-up, and small-scale turbulent eddies. 相似文献
16.
Yu. G. Gubarev 《Technical Physics》2011,56(3):345-350
The problem of linear stability of steady-state axisymmetric shear jet flows of an inviscid ideally conducting incompressible
liquid with a free surface and “frozen-in” azimuthal magnetic field is analyzed. The sufficient conditions for theoretical
(on semi-infinite time intervals) and practical (on finite time intervals) instability of these flows relative to small axisymmetric
long-wave perturbations are obtained by the direct Lyapunov method. An a priori lower estimate indicating (at least) an exponential
increase with time of small perturbations under investigation is constructed in the case when these conditions are valid for
theoretical as well as practical instability. In addition, an illustrative analytic example of steady-state flows under investigation
and small axisymmetric long-wave perturbations superimposed on them is constructed (according to our estimate, these perturbations
increase with time). 相似文献
17.
M. A. Pedrosa C. Hidalgo E. Calderon A. Alonso R. O. Orozco J. L. De Pablos TJ-II team P. Balan 《Czechoslovak Journal of Physics》2005,55(12):1579-1587
The influence of plasma density and edge gradients in the development of perpendicular sheared flow has been investigated
in the plasma edge region of the TJ-II stellarator. It has been experimentally observed that the generation of spontaneous
perpendicular sheared flow (i.e. the naturally occurring shear layer) requires a minimum plasma density or gradient. It has
been found that there is a coupling between the onset of sheared flow development and an increase in the level of plasma edge
turbulence; once sheared flow is fully developed the level of fluctuations and turbulent transport slightly decreases whereas
edge gradients and plasma density increase. The resulting shearing rate is close to the one required to trigger a transition
to improved confinement regimes with reduction of edge turbulence, showing that spontaneous sheared flows and fluctuations
keep themselves near marginal stability.
Presented at the Workshop “Electric Fields, Structures and Relaxation in Edge Plasmas”, Tarragona, Spain, July 3–4, 2005. 相似文献
18.
The existence of surface polaritons in a dielectric at a boundary with an ideal metal or superconductor in a static electric
field is predicted. The frequency regions in which polaritons exist are substantially different for opposite orientations
of the electric field, so that a change in the direction of the field signifies “switching on” or “switching off” of surface
polaritons with a fixed frequency.
Pis'ma Zh. éksp. Teor. Fiz. 68, No. 12, 876–880 (25 December 1998) 相似文献
19.
V. Ya. Shur E. L. Rumyantsev V. P. Kuminov A. L. Subbotin V. L. Kozhevnikov 《Physics of the Solid State》1999,41(2):269-273
Barkhausen pulses generated in stepped motion of a single plane domain boundary (PDB) are investigated experimentally in single-crystalline
wafers of the extrinsic ferroelastic ferroelectric gadolinium molybdate containing artificial pinning centers of the “field
inhomogeneity” type near the edges of the sample. Two scenarios of the evolution of a PDB in interaction with “defects” are
proposed on the basis of analyzing the shape of the pulses in a linearly increasing field: small changes of the pulse shape
in a weak field and the generation of wedge domains in a strong field. The proposed mechanism of PDB motion due to the generation
of steps near the edge of the sample and their longitudinal motion provides a means for explaining the experimentally observed
linear field dependence of the PDB velocity and for determining the velocity of the steps.
Fiz. Tverd. Tela (St. Petersburg) 41, 301–305 (February 1999) 相似文献
20.
Local heat transfer to a rotating disk in the presence of an imposed axial flow has been studied using thermochromic liquid crystals and the transient heating technique. Preliminary measurements were made for a smooth disk, for which the experimental data encompassed the laminar boundary layer, the transitional zone, and the beginning of the turbulent region. Measurements were then made for arrangements in which a circular trip wire installed concentrically on the disk was used to disturb the boundary layer. The main topic of the investigation concerned convective heat transfer to disks with concentric circular ribs of a rectangular cross section. Three roughness configurations have been investigated, and the results have been compared with data for a smooth disk. The ribs caused an early transition from laminar flow to turbulent flow. Otherwise the augmentation of heat transfer by the circular ribs was rather modest, except with high axial flows and low rotational speeds, when the velocities across the ribs would have been of a similar order of magnitude to the tangential velocities between the ribs. 相似文献