Increasing effectiveness of early warning through smart ICT

Skrbek, Jan; Lamr, Marian

doi:10.1109/icoict.2015.7231415

Cited by 2 publications

(3 citation statements)

References 4 publications

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“…Second sound is attenuated due to the scattering of thermal excitations (which constitute the normal fluid) by quantized vortices; from measuring the reduction in amplitude of the second sound signal when the heater is switched on, the vortex line density can be estimated. With higher harmonics of the second sound, it is possible, in principle, to crudely measure the structure of the tangle across the channel [39]. Given the results presented here, it is reasonable to consider that the transition to the turbulent normal fluid state could be detected, without directly imaging the flow, but through monitoring of the homogeneity of the vortex tangle.…”

Section: The Ti To Tii Transitionmentioning

confidence: 98%

Thermal Counterflow in a Periodic Channel with Solid Boundaries

Baggaley

Laurie

2014

J Low Temp Phys

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We perform numerical simulations of finite temperature quantum turbulence produced through thermal counterflow in superfluid 4 He, using the vortex filament model. We investigate the effects of solid boundaries along one of the Cartesian directions, assuming a laminar normal fluid with a Poiseuille velocity profile, whilst varying the temperature and the normal fluid velocity. We analyze the distribution of the quantized vortices, reconnection rates and quantized-vorticity production as a function of the wall-normal direction. We find that the quantized vortex lines tend to concentrate close to the solid boundaries with their position depending only on temperature and not on the counterflow velocity. We offer an explanation of this phenomenon by considering the balance of two competing effects, namely the rate of turbulent diffusion of an isotropic tangle near the boundaries and the rate of quantized-vorticity production at the centre. Moreover, this yields the observed scaling of the position of the peak vortex line density with the mutual friction parameter. Finally we provide evidence that upon the transition from laminar to turbulent normal fluid flow, there is a dramatic increase in the homogeneity of the tangle, which could be used as an indirect measure of the transition to turbulence in the normal fluid component for experiments.

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Section: The Ti To Tii Transitionmentioning

confidence: 98%

Thermal Counterflow in a Periodic Channel with Solid Boundaries

Baggaley

Laurie

2014

J Low Temp Phys

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“…Using Eqs. (18) and (19) to describe the image vortex ring is a suitable approximation only when the vortex ring is close to the boundary. Although Samuels obtained velocity matching by using these processes, this dynamics is not realistic.…”

Section: Velocity Matchingmentioning

confidence: 99%

“…Numerical studies of coflow could find other characteristic features that differ from those of thermal counterflow turbulence, in addition to the above observations. Note that the normal fluid flow as well as the superfluid flow is thought to be turbulent in the experiment 19 .…”

Section: Introductionmentioning

confidence: 99%

Coflow turbulence of superfluidHe4in a square channel: Vortices trapped on a cylindrical attractor

Ikawa

Tsubota

2016

Phys. Rev. B

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We perform a numerical simulation of the dynamics of quantized vortices produced by coflow in a square channel using the vortex filament model. Unlike the situation in thermal counterflow, where the superfluid velocity vs and normal fluid velocity vn flow in opposite directions, in coflow, vs and vn flow in the same direction. Quantum turbulence in thermal counterflow has been long studied theoretically and experimentally, and its various features have been revealed. In recent years, an experiment on quantum turbulence in coflow has been performed to observe different features of thermal counterflow. By supposing that vs is uniform and vn takes the Hagen-Poiseuille profile, which is different from the experiment where vn is thought to be turbulent, we calculate the coflow turbulence. Vortices preferentially accumulate on the surface of a cylinder for vs ≃ vn by mutual friction; namely, the coflow turbulence has an attractor. How strongly the vortices are attracted depends on the temperature and velocity. The length of the vortices increases as the vortices protruding from the cylindrical attractor continue to wrap around it. As the vortices become dense on the attractor, they spread toward its interior by their repulsive interaction. Then, the superfluid velocity profile induced by the vortices gradually mimics the normal-fluid velocity profile. This is an indication of velocity matching, which is an important feature of coflow turbulence.

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Increasing effectiveness of early warning through smart ICT

Cited by 2 publications

References 4 publications

Thermal Counterflow in a Periodic Channel with Solid Boundaries

Thermal Counterflow in a Periodic Channel with Solid Boundaries

Coflow turbulence of superfluidHe4in a square channel: Vortices trapped on a cylindrical attractor

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