331 research outputs found
Acceleration statistics in thermally driven superfluid turbulence
New methods of flow visualization near absolute zero have opened the way to
directly compare quantum turbulence (in superfluid helium) to classical
turbulence (in ordinary fluids such as air or water) and explore analogies and
differences. We present results of numerical simulations in which we examine
the statistics of the superfluid acceleration in thermal counterflow. We find
that, unlike the velocity, the acceleration obeys scaling laws similar to
classical turbulence, in agreement with a recent quantum turbulence experiment
of La Mantia et al.Comment: 5 pages, 5 figures, to appear in PR
Vortex density fluctuations in quantum turbulence
We compute the frequency spectrum of turbulent superfluid vortex density
fluctuations and obtain the same Kolmogorov scaling which has been observed in
a recent experiment in Helium-4. We show that the scaling can be interpreted in
terms of the spectrum of reconnecting material lines. The calculation is
performed using a vortex tree algorithm which considerably speeds up the
evaluation of Biot-Savart integrals.Comment: 7 Pages, 7 figure
Quantum vortex reconnections
We study reconnections of quantum vortices by numerically solving the
governing Gross-Pitaevskii equation. We find that the minimum distance between
vortices scales differently with time before and after the vortex reconnection.
We also compute vortex reconnections using the Biot-Savart law for vortex
filaments of infinitesimal thickness, and find that, in this model,
reconnection are time-symmetric. We argue that the likely cause of the
difference between the Gross-Pitaevskii model and the Biot-Savart model is the
intense rarefaction wave which is radiated away from a Gross-Pitaeveskii
reconnection. Finally we compare our results to experimental observations in
superfluid helium, and discuss the different length scales probed by the two
models and by experiments.Comment: 23 Pages, 12 Figure
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