Dissipation enhancement from a single vortex reconnection in superfluid helium

Hänninen, Risto

doi:10.1103/physrevb.88.054511

Cited by 23 publications

(19 citation statements)

References 43 publications

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“…This phenomenon is illustrated numerically in a model system of two vortex rings, reconnecting in the presence of mutual friction damping, which countinuously decreases the total energy and momentum of the system (35). After the reconnection, Kelvin waves are excited, and the oscillating motion causes substantial extra energy dissipation, whereas the rate of momentum change is essentially not affected by the reconnection event.…”

Section: Energy Dissipation and Momentum Transfermentioning

confidence: 96%

Quantum turbulence in superfluids with wall-clamped normal component

Eltsov

Hänninen

Krusius

2014

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

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In Fermi superfluids, such as superfluid 3 He, the viscous normal component can be considered to be stationary with respect to the container. The normal component interacts with the superfluid component via mutual friction, which damps the motion of quantized vortex lines and eventually couples the superfluid component to the container. With decreasing temperature and mutual friction, the internal dynamics of the superfluid component becomes more important compared with the damping and coupling effects from the normal component. As a result profound changes in superfluid dynamics are observed: the temperature-dependent transition from laminar to turbulent vortex motion and the decoupling from the reference frame of the container at even lower temperatures.superfluid Reynolds number | vortex tension | vortex front | rotating flow | pipe flow I n this paper, we consider the motion of quantized vortices in superfluids, where the normal component is clamped to the walls of the container; that is, it is stationary in a reference frame moving with the wall. This situation can be experimentally realized in superfluid 3 He. In such systems, turbulent motion can occur only in the superfluid component and thus, in principle, is easier to analyze. Here the role of the normal fluid is twofold: first, it provides friction in the superfluid motion, which is mediated by quantized vortices and works over a wide range of length scales. Second, it provides a coupling to the container walls, which acts uniformly over the whole volume of the superfluid. This situation is quite unlike classical turbulence, where viscous dissipation operates only at the small Kolmogorov scale and coupling to the walls is provided by thin boundary layers.As a result, a variety of new phenomena is observed in experiments and numerical simulations as a function of temperature. These phenomena are controlled by the normal-fluid density. At the highest temperatures, turbulent motion is suppressed completely. When the temperature decreases, a sharp transition to turbulence is seen. The transition can be characterized by a superfluid Reynolds number, which is composed of the internal friction parameters of the superfluid and is independent of velocity. When turbulence is triggered by a localized perturbation of the laminar flow, the critical value of the Reynolds number is found to scale with the strength of the perturbation.When the temperature decreases further, friction from the normal component rapidly vanishes. The overall dissipation rate in quantum turbulence remains nevertheless finite, owing to the contribution from the turbulent energy cascade, and reaches a temperatureindependent value in the zero-temperature limit. This zero-temperature dissipation can be characterized by an effective viscosity or friction. It is found, however, that coupling to the walls is not essentially improved by the turbulence and can potentially become very small. At the lowest temperatures the concept of a single effective friction breaks down; for the proper descriptio...

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Section: Energy Dissipation and Momentum Transfermentioning

confidence: 96%

Quantum turbulence in superfluids with wall-clamped normal component

Eltsov

Hänninen

Krusius

2014

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

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“…If we consider the analytical model (which is based on earlier numerical work) for the vortex shape before the reconnection [11], we get further support for Eq. (7). This estimate for the prereconnection vortex shape indicates that the cusp sharpens until the minimum distance reaches the core size (after which the filament model is not valid any more) such that eventually the region, where the curvature is of the order of the inverse core radius, is also of the order of the core diameter.…”

Section: B Sharp Cusp and Its Effect On Rms Curvaturementioning

confidence: 96%

“…Our numerics is described in more detail in Ref. [7], where we analyzed a similar situation of reconnecting vortex rings but concentrated on the dissipation due to mutual friction.…”

Section: Modelmentioning

confidence: 99%

“…The initial distance between the two vortices is 0.1R, causing that at T = 0 they will reconnect approximately at 1.696 s. For dynamics, see Ref. [7]. Our reconnection method is rather standard: We reconnect the vortex segments when the mini-mum distance becomes smaller than 0.8∆ξ min , where ∆ξ min is the minimum point separation tolerated.…”

Section: A Numerical Setupmentioning

confidence: 99%

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Kelvin waves from vortex reconnection in superfluid helium at low temperatures

Hänninen

2015

Phys. Rev. B

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We report on the analysis of the root mean square curvature as a function of the numerical resolution for a single reconnection of two quantized vortex rings in superfluid helium. We find a similar scaling relation as reported in the case of decaying thermal counterflow simulations by L. Kondaurova et al. There the scaling was related to the existence of a Kelvin-wave cascade which was suggested to support the L'vov-Nazarenko spectrum. Here we provide an alternative explanation that does not involve the Kelvin-wave cascade but is due to the sharp cusp generated by a reconnection event in a situation where the maximum curvature is limited by the computational resolution. We also suggest a method for identifying the Kelvin spectrum based on the decay of the rms curvature by mutual friction. Our vortex filament simulation calculations show that the spectrum of Kelvin waves after the reconnection is not simply n(k) ∝ k −η with constant η. At large scales the spectrum seems to be close to the Vinen prediction with η = 3 but becomes steeper at smaller scales.

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“…Recently, there were many theoretical investigations into reconnections of quantized vortex lines [3,4,[9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. In particular, for acute angles between two antiparallel reconnecting vortex lines the generation of a cascade of small vortex rings was predicted [20,21,31].…”

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confidence: 98%

Reconnections of Quantized Vortex Rings in SuperfluidHe4at Very Low Temperatures

et al. 2014

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Collisions in a beam of unidirectional quantized vortex rings of nearly identical radii R in superfluid 4He in the limit of zero temperature (0.05 K) were studied using time-of-flight spectroscopy. Reconnections between two primary rings result in secondary vortex loops of both smaller and larger radii. Discrete steps in the distribution of flight times, due to the limits on the earliest possible arrival times of secondary loops created after either one or two consecutive reconnections, are observed. The density of primary rings was found to be capped at the value 500 cm-2R-1 independent of the injected density. This is due to collisions between rings causing the piling up of many other vortex rings. Both observations are in quantitative agreement with our theory.

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Dissipation enhancement from a single vortex reconnection in superfluid helium

Cited by 23 publications

References 43 publications

Quantum turbulence in superfluids with wall-clamped normal component

Quantum turbulence in superfluids with wall-clamped normal component

Kelvin waves from vortex reconnection in superfluid helium at low temperatures

Reconnections of Quantized Vortex Rings in SuperfluidHe4at Very Low Temperatures

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