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Abstracts
P3.12
Turbulent
4
He flows generated by an oscillating grid and visualized
by particle tracking
ˇSvanˇcara Patrik, Duda Daniel, La Mantia Marco, Rotter Miloˇs and Skrbek
Ladislav
Charles University, Faculty of Mathematics and Physics, Ke Karlovu 3, 121 16
Prague 2, Czech Republic
The dynamics of micron-sized solid deuterium particles is studied experimentally
in turbulent flows of both He I and He II by visualization. Turbulence in both
phases is mechanically generated by a grid, consisting of equally spaced circular
holes, oscillating at frequencies up to 3 Hz. We find that, in He II, at length
scales larger than the mean intervortex distance, particle velocity statistical
distributions closely resemble those obtained in viscous He I. Our results
reinforce the idea that turbulent flows of He II mimic viscous flows, at large
enough length scales.
We acknowledge the support of Charles University under GAUK grant no.
1109416.
P3.13
The decay of thermal counterflow turbulence in superfluid
4
He from
small heat currents
J. Gao(1,2), W. Guo(1,2), S. Yui(3), M. Tsubota(3), W. F. Vinen(4)
1) National High Magnetic Field Laboratory, 1800 East Paul Dirac Drive,
Tallahassee, FL 32310, USA
2) Machanical Engineering Department, Florida State University, Tallahassee,
FL 32310, USA
3) Department of Physics, Osaka City University, 3-3-138 Sugimoto,
Sumiyoshi-Ku, Osaka 558-8585, Japan
4) School of Physics and Astronomy, University of Birmingham, Birmingham
B15 2TT, UK
Quantum turbulence is easily generated in superfluid
4
He in the presence of
a thermally-generated counterflow of the two fluids. For small heat fluxes the
turbulence is present only in the superfluid component and takes the form of
a random tangle of quantized vortex lines. When the heat flux is removed the
vortex line density,
L
, decays according to the equation
dL/dt
=
−
(
X
2
κ/
2
π
)
L
2
,
where
κ
is the quantum of circulation and
X
2
is a dimensionless function of
temperature. New experimental measurements of
X
2
are presented, together
with new values of this parameter derived from computer simulations. Both are
compared with values derived from a theory due to Vinen and Niemela.
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