23 research outputs found
Probing quantum and classical turbulence analogy through global bifurcations in a von K\'arm\'an liquid Helium experiment
We report measurements of the dissipation in the Superfluid Helium high
REynold number von Karman flow (SHREK) experiment for different forcing
conditions, through a regime of global hysteretic bifurcation. Our
macroscopical measurements indicate no noticeable difference between the
classical fluid and the superfluid regimes, thereby providing evidence of the
same dissipative anomaly and response to asymmetry in fluid and superfluid
regime. %In the latter case, A detailed study of the variations of the
hysteretic cycle with Reynolds number supports the idea that (i) the stability
of the bifurcated states of classical turbulence in this closed flow is partly
governed by the dissipative scales and (ii) the normal and the superfluid
component at these temperatures (1.6K) are locked down to the dissipative
length scale.Comment: 5 pages, 5 figure
Low Temperature Gaseous Helium and very High Turbulence Experiments
Cryogenic gaseous helium gives access to extreme turbulent experimental conditions. The very high cooling helium flow rates available at CERN have been used to reach Reynolds numbers up to Re ~ 10**7 in a round jet experiment. First results are discussed
A Cryogenic High-Reynolds Turbulence Experiment at CERN
The potential of cryogenic helium flows for studying high-Reynolds number turbulence in the laboratory has been recognised for a long time and implemented in several small-scale hydrodynamic experiments. With its large superconducting particle accelerators and detector magnets, CERN, the European Laboratory for Particle Physics, has become a major world center in helium cryogenics, with several large helium refrigerators having capacities up to 18 kW @ 4.5 K. Combining a small fraction of these resources with the expertise of three laboratories at the forefront of turbulence research, has led to the design, swift implementation, and successful operation of GReC (Grands Reynolds Cryogéniques) a large axisymmetric turbulent-jet experiment. With flow-rates up to 260 g/s of gaseous helium at ~ 5 K and atmospheric pressure, Reynolds numbers up to 107 have been achieved in a 4.6 m high, 1.4 m diameter cryostat. This paper presents the results of the first runs and describes the experimental set-up comprehensively equipped with "hot" wire micro-anemometers, acoustic scattering vorticity measurements and a large-bandwidth data acquisition system
Intermittency in a turbulent low temperature gaseous helium jet
We analyse experimental velocity measurements on the axis of a low
temperature gaseous helium jet. From independent increments arguments, we
reproduce the behaviour of structure functions. We show where this
approach fails and how the intermittency phenomenon is a small correction.
The physical arguments under the multiplicative cascade models for this
intermittency imply an acceleration of this cascade close to the
dissipative range, which we are able to evidence. This acceleration could
be responsible of the apparent Extended Self Similarity between structure
functions of various orders
EXPERIMENTAL CONSIDERATIONS ON PRODUCING HIGHLY POLARIZED LIQUID 3He IN A MATRIX OF SOLID 4He
On rappelle brièvement les résultats obtenus dans deux expériences où des gouttes de 3He étaient formées dans 4He solide. Ces expériences montrent que de telles conditions sont favorables pour la production de 3He liquide fortement polarisé quasi-stable. Une solution solide de 3He dilué dans 4He est proposée comme devant être un système prometteur pour l'obtention expérimentale de 3He liquide hautement polarisé en utilisant une décompression analogue à celle proposée par Castaing et Nozières.Two experiments are briefly reviewed in which droplets of 3He were formed in solid 4He. These experiments indicate such conditions are favorable for the production of quasi-stable highly polarized liquid 3He. A solid solution of dilute 3He in 4He is proposed as a promising system to produce experimentally realizable highly polarized liquid 3He using the Castaing-Nozières decompression
Nuclear-induced resistivity drop in the Kondo alloy Au-171 Yb
The electrical resistivities of monoisotopic dilute alloys of Au- 171Yb and Au-174Yb have been measured down to 18 mK. A resistivity drop is observed in Au-171Yb, below 90 mK. This effect is shown to result from the magnetic hyperfine coupling in 171Yb which splits the electro-nuclear levels into a singlet ground state and a triplet excited state. A simple model is proposed which accounts for the experimental results.La résistivité électrique d'alliages dilués monoisotopiques d'Au- 171Yb et de Au-174Yb a été mesurée jusqu'à 18 mK. Dans l'Au-171Yb, on observe une chute de résistivité en dessous de 90 mK. On montre que cet effet résulte du couplage hyperfin magnétique dans l'171Yb qui lève la dégénérescence des niveaux électronucléaires en produisant un état fondamental singulet et un état excité triplet. On propose un modèle simple qui rend compte des résultats expérimentaux
Side wall effects in Rayleigh Bénard experiments
In Rayleigh Bénard experiments, the side wall conductivity is traditionally
taken into account by subtracting the empty cell heat conductivity from the
measured one. We present a model showing that the correction to apply could be
considerably larger. We compare to experiments and find good agreement. One of
the consequences is that the Nusselt behavior for could be closer
to than currently assumed. Also, the wall effect can
appear as a continuous change in the γ exponent