Free Decay of Superfluid Turbulence

Milliken, F. P.; Schwarz, K. W.; Smith, Charles W.

doi:10.1103/physrevlett.48.1204

Cited by 50 publications

(34 citation statements)

References 13 publications

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“…Although the transient behavior generally refers to both the growth and decay process, this paper considers only the decay of the VT after the driving velocity is suddenly reduced to zero. The early measurements by Vinen 5 and the later ones 16,17 observed a decay of the VT which was consistent with the Vinen's equation (1) with only the decay term, although Schwarz and Rozen 17 coupled the Vinen's equation with the hydrodynamical equations of the normal flow and the superflow in order to explain a slow decay following an initial rapid decay they observed. Apart from these experiments on thermal counterflow, the decay of vorticity in turbulence generated by towing a grid was studied recently.…”

Section: Introductionsupporting

confidence: 50%

Dynamics of vortex tangle without mutual friction in superfluid4He

2000

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A recent experiment has shown that a tangle of quantized vortices in superfluid 4 He decayed even at mK temperatures where the normal fluid was negligible and no mutual friction worked. Motivated by this experiment, this work studies numerically the dynamics of the vortex tangle without the mutual friction, thus showing that a self-similar cascade process, whereby large vortex loops break up to smaller ones, proceeds in the vortex tangle and is closely related with its free decay. This cascade process which may be covered with the mutual friction at higher temperatures is just the one at zero temperature Feynman proposed long ago. The full Biot-Savart calculation is made for dilute vortices, while the localized induction approximation is used for a dense tangle. The former finds the elementary scenario: the reconnection of the vortices excites vortex waves along them and makes them kinked, which could be suppressed if the mutual friction worked. The kinked parts reconnect with the vortex they belong to, dividing into small loops. The latter simulation under the localized induction approximation shows that such cascade process actually proceeds self-similarly in a dense tangle and continues to make small vortices. Considering that the vortices of the interatomic size no longer keep the picture of vortex, the cascade process leads to the decay of the vortex line density. The presence of the cascade process is supported also by investigating the classification of the reconnection type and the size distribution of vortices. The decay of the vortex line density is consistent with the solution of the Vinen's equation which was originally derived on the basis of the idea of homogeneous turbulence with the cascade process. The cascade process revealed by this work is an intrinsic process in the superfluid system free from the normal fluid. The obtained result is compared with the recent Vinen's theory which discusses the Kelvin wave cascade with sound radiation.67.40.Vs, 67.40.Bz

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Section: Introductionsupporting

confidence: 50%

Dynamics of vortex tangle without mutual friction in superfluid4He

2000

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“…Helium ions have been successfully used to detect quantum vortices in 4 He-for example, to investigate the decay of inhomogeneous quantum turbulence created by ultrasonic transducers at about 1:5K (24). An improved technique based on negative ions has been recently introduced for measurements of decaying quantum turbulence below 1 K (25,26).…”

Section: Experimental Methods For Quantum Turbulencementioning

confidence: 99%

“…The Madelung transformation makes the hydrodynamics interpretation of the wave function ψ apparent, yielding the classical continuity equation and a modified Euler equation. It differs from the classical Euler equation because of the presence of the so-called quantum pressure, which, differentiating a superflow from a perfect Euler flow, is responsible for vortex reconnections (31), for sound pulses at reconnection events (32), and for the nucleation of vortices near a boundary (e.g., an ion) (33) or a strong density variation (e.g., cavitation) (24,34).…”

Section: Theoretical Models Of Quantum Turbulencementioning

confidence: 99%

Introduction to quantum turbulence

Barenghi

Skrbek

Sreenivasan

2014

Proc. Natl. Acad. Sci. U.S.A.

284

264

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The term quantum turbulence denotes the turbulent motion of quantum fluids, systems such as superfluid helium and atomic Bose-Einstein condensates, which are characterized by quantized vorticity, superfluidity, and, at finite temperatures, two-fluid behavior. This article introduces their basic properties, describes types and regimes of turbulence that have been observed, and highlights similarities and differences between quantum turbulence and classical turbulence in ordinary fluids. Our aim is also to link together the articles of this special issue and to provide a perspective of the future development of a subject that contains aspects of fluid mechanics, atomic physics, condensed matter, and low-temperature physics.Turbulence is a spatially and temporally complex state of fluid motion. Five centuries ago, Leonardo da Vinci noticed that water falling into a pond creates eddies of motion. Today, turbulence still provides physicists, applied mathematicians, and engineers with a continuing challenge. Leonardo realized that the motion of water shapes the landscape. Today's researchers appreciate that many physical processes, from the generation of the Galactic magnetic field to the efficiency of jet engines, depend on turbulence.The articles in this collection are devoted to a special form of turbulence known as quantum turbulence (1-3), which appears in quantum fluids. Quantum fluids differ from ordinary fluids in three respects: (i) they exhibit two-fluid behavior at nonzero temperature or in the presence of impurities, (ii) they can flow freely, without the dissipative effect of viscous forces, and (iii) their local rotation is constrained to discrete vortex lines of known strength (unlike the eddies in ordinary fluids, which are continuous and can have arbitrary size, shape, and strength). Superfluidity and quantized vorticity are extraordinary manifestations of quantum mechanics at macroscopiclength scales.Recent experiments have highlighted quantitative connections, as well as fundamental differences, between turbulence in quantum fluids and turbulence in ordinary fluids (classical turbulence). The relation between the two forms of turbulence is indeed a common theme in the articles collected here. Because different scientific communities (lowtemperature physics, condensed-matter physics, fluid dynamics, and atomic physics) have contributed to progress in quantum turbulence, † the aim of this article is to introduce the main ideas in a coherent way. Quantum FluidsIn this series of articles, we shall be concerned almost exclusively with superfluid 4 He, the B-phase of superfluid 3 He, and, to a lesser extent, with ultracold atomic gases. These systems exist as fluids at temperatures on the order of a Kelvin, milliKelvin, and microKelvin, respectively.‡ Their constituents are either bosons (such as 4 He atoms with zero spin) or fermions (such as 3 He atoms with spin 1/2). This difference is fundamental: the former obey Bose-Einstein statistics and the latter Fermi-Dirac quantum statistics.Let us consider an...

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“…One can estimate the effect of thickness variations on the output power. If the separation between active layers is not exactly one acoustic wavelength, the 41 wave produced in that layer will have some phase offset relative to the entering wave. The acoustic amplitude at the substrate would then be:…”

Section: Extension To Higher Frequenciesmentioning

confidence: 99%

“…This process should be a slow one. 41 Experiments using multiple pulses showed, however, that the pulses were completely independent-noninterfering on time scales as short as 100 nanoseconds.…”

Section: Analysis Of Datamentioning

confidence: 99%