摘要 :
A theory is developed to describe grid turbulence in a superfluid in the case where the normal fluid is held stationary, as would be the case for superfluid ~3He-B in which the normal fluid is very viscous. The theory is a straigh...
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A theory is developed to describe grid turbulence in a superfluid in the case where the normal fluid is held stationary, as would be the case for superfluid ~3He-B in which the normal fluid is very viscous. The theory is a straightforward development of earlier work, reviewed by Vinen and Niemela [J. Low Temp. Phys. 128, 167 (2002)], and it shows that on large length scales the turbulence is strongly damped by mutual friction. A comparison is made with recent work by Volovik and his colleagues [G. E. Volovik, JETP Lett. 78, 533 (2003); G. E. Volovik, J. Low Temp. Phys. (to be published); and L'vov, Nazarenko, and Volovik, JETP Lett, (to be published)], which was developed while our work was in progress.
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We present experimental, numerical, and theoretical studies oi' a vortex front propagating into a region of vortex-free flow of rotating superfluid ~3He-B. We show that the nature of the front changes from laminar through quasicla...
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We present experimental, numerical, and theoretical studies oi' a vortex front propagating into a region of vortex-free flow of rotating superfluid ~3He-B. We show that the nature of the front changes from laminar through quasiclassical turbulent to quantum turbulent with decreasing temperature. Our experiment provides the first direct measurement of the dissipation rate in turbulent vortex dynamics of ~3He-B and demonstrates that the dissipation becomes mutual-friction independent with decreasing temperature, and it is strongly suppressed when the Kelvin-wave cascade on vortex lines is predicted to be involved in the turbulent energy transfer to smaller length scales.
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We study a twisted vortex bundle where quantized vortices form helices circling around the axis of the bundle in a "force-free" configuration. Such a state is created by injecting vortices into a rotating vortex-free superfluid. U...
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We study a twisted vortex bundle where quantized vortices form helices circling around the axis of the bundle in a "force-free" configuration. Such a state is created by injecting vortices into a rotating vortex-free superfluid. Using continuum theory we determine the structure and the relaxation of the twisted state. This is confirmed by numerical calculations. We also present experimental evidence of the twisted vortex state in superfluid ~3He-B.
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The proximity effect causes the existence of some transition area with the gradual variation of the density of superfluid component instead of the sharp boundary at the level where the hydrostatic pressure realizes the phase trans...
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The proximity effect causes the existence of some transition area with the gradual variation of the density of superfluid component instead of the sharp boundary at the level where the hydrostatic pressure realizes the phase transition He Ⅱ-He Ⅰ. In the microgravity environment the characteristic length of this effect increases, and more convenient conditions arise for measurements in the transition area. The problem of the expansion of thermodynamical potential in power series in the vicinity of He Ⅱ-He Ⅰ interface is considered. The critical values of the size of the superfluid area are determined.
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The unstable states (including those related to self-accelerations of pulsars) in which the mutual friction causes an irreversible motion of vortices is considered.
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The paper is concerned with the interpretation of many experiments that have been reported recently on the production of quantum turbulence by oscillating spheres, wires and grids in both ~4He and ~3He-B at temperatures so low tha...
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The paper is concerned with the interpretation of many experiments that have been reported recently on the production of quantum turbulence by oscillating spheres, wires and grids in both ~4He and ~3He-B at temperatures so low that there is a negligible fraction of normal fluid. The experimental results are compared with those obtained in analogous experiments with classical fluids and with preliminary simulations of the quantum turbulence. Particular attention is paid to observed values of drag coefficients and to the very different critical velocities observed in ~4He and ~3He. It is tentatively concluded that in the case of ~4He behavior may well be similar to that observed in the classical analogues, with relatively small changes when the characteristic size of the oscillating structure is not large compared with the quantized vortex spacing, but that in the case of ~3He behavior is very different and due perhaps to very rapid intrinsic nucleation of the quantized vortices.
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Turbulent flow of superfluid ~4He at mK temperatures around an oscillating microsphere is known to be unstable at low driving forces, switching intermittently between turbulent and laminar phases. The lifetimes of the turbulent ph...
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Turbulent flow of superfluid ~4He at mK temperatures around an oscillating microsphere is known to be unstable at low driving forces, switching intermittently between turbulent and laminar phases. The lifetimes of the turbulent phases are exponentially distributed, and the mean lifetimes grow exponentially with the square of the driving force. These experimental results are attributed to statistical fluctuations of the density L of the vortex line length. As a result, a normal probability distribution of L~2 is found having a standard deviation of 2.9 X 10~(14) m~(-4) and a spectral bandwidth Δω ≈ 13 s~(-1).
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We numerically study the evolution of a small turbulent region of quantised vorticity in superfluid helium, a regime which can be realised in the laboratory. We show that the turbulence achieves a fluctuating steady-state in terms...
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We numerically study the evolution of a small turbulent region of quantised vorticity in superfluid helium, a regime which can be realised in the laboratory. We show that the turbulence achieves a fluctuating steady-state in terms of dynamics (energy), geometry (length, writhing) and topology (linking). We show that, at any instant, the turbulence consists of many unknots and few large loops of great geometrical and topological complexity.
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We present a derivation of the transverse force acting on a hydrodynamic vortex in the presence of a sound wave from a global solution of the scattering problem, using the method of matched asymptotic expansions. The solution pres...
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We present a derivation of the transverse force acting on a hydrodynamic vortex in the presence of a sound wave from a global solution of the scattering problem, using the method of matched asymptotic expansions. The solution presented includes a detailed treatment of the interaction of the incident wave with the vortex core, and is free from the singularities in the momentum exchange between vortex and sound wave which have led to contradictory results for the value of the transverse force in the literature.
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The motions of superfluid vortices attached to a boundary are investigated in alternating currents by using a vibrating wire. The attached vortices appear to form a layer on the wire and enhance the mass of the wire, even for low ...
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The motions of superfluid vortices attached to a boundary are investigated in alternating currents by using a vibrating wire. The attached vortices appear to form a layer on the wire and enhance the mass of the wire, even for low velocity currents. In turbulence, chaotic motions of vortices such as entanglement and reconnection reduce the thickness of the layer in spite of the fact that the vortices unstably expand. When turbulence subsides, the attached vortices appear to shrink, with the degree of shrinking influenced by thermal excitations in the superfluid.
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