Bulletin of the American Physical Society
61st Annual Meeting of the APS Division of Fluid Dynamics
Volume 53, Number 15
Sunday–Tuesday, November 23–25, 2008; San Antonio, Texas
Session BW: Mini-Symposium: Flow Visualization in Low Temperature Helium |
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Chair: Steven van Scriver, Florida State University Room: 004 |
Sunday, November 23, 2008 10:30AM - 10:52AM |
BW.00001: Future prospects for Flow Visualization in Low Temperature Helium Invited Speaker: The techniques discussed in the preceding papers in this Minisymposium on Flow Visualization in Low Temperature Helium will be reviewed in the light of future needs, especially in connection with experimental evidence relating to important questions arising in the study of quantum turbulence. Quantum turbulence is a form of turbulence found in superfluid systems (superfluid $^4$He and superfluid $^3$He-B), where flow is strongly affected by quantum effects, and it poses especially difficult and challenging problems in connection with visualization, in terms of both interpretation and the choice of seed particle. At the same time there is an great need for information that only visualization can provide. Future prospects will be surveyed. [Preview Abstract] |
Sunday, November 23, 2008 10:52AM - 11:14AM |
BW.00002: Classical Vs. Superfluid Turbulence Invited Speaker: Thanks to a zero-viscosity, superfluids offer a unique testing ground for hydrodynamic models, in particular for turbulence ones. In Kolmogorov's turbulence model, viscosity is well known to damp the kinetic energy of the smallest eddies, and thus to introduce a cut-off at one end of the turbulent cascade. Significant differences between this ``classical'' turbulence and the turbulence of a superfluid are therefore expected, but --surprisingly- most experiments rather evidenced strong similarities. We will give an overview of a set of experiments designed to compare in details the classical versus superfluid turbulences, up to a record mass flow of superfluid (700g/s of He @ 1.6K). Then, we will focus on some unexpected vorticity measurements, which can be interpreted assuming that the superfluid vortices are passively advected by the largest scales of the flow, in contrast with the ``classical'' turbulence counterpart. Numerical simulations -based on regular DNS- will be presented to complete this interpretation. In collaboration with C. Barenghi, University of Newcastle; B. Castaing and E. Lev\`eque, ENSL, Lyon; S. David, IEF, CNRS, Orsay; B. Rousset, SBT/CEA, Grenoble; and P. Tabeling, H. Willaime MMN, ESPCI, Paris. [Preview Abstract] |
Sunday, November 23, 2008 11:14AM - 11:36AM |
BW.00003: Measurement of superfluid thermal counterflow jet using PIV Invited Speaker: The particle image velocimetry (PIV) technique was applied to the measurement of the thermal counterflow jet of superfluid He II in the superfluid turbulent state. Neutrally buoyant hydrogen-deuterium micro solid particles were used as tracer for PIV, which measures the velocity of the normal component. The velocity profile and the spatial decay of the jet velocity were compared with those of round turbulent jets of viscous fluids. The PIV velocity was compared with the theoretical prediction. It was found that the PIV velocity was always smaller than the theoretical prediction and this reduction ratio depended on the temperature, strongly in higher temperature range above 2.0 K and weakly below 2.0 K. It is considered that this results from the interaction of particles and/or the normal fluid component with high density quantized vortices. In collaboration with Takeshi Takakoshi, Motoki Maeda, and Naoki Yokota, University of Tsukuba. [Preview Abstract] |
Sunday, November 23, 2008 11:36AM - 11:58AM |
BW.00004: Particle Image Velocimetry in Superfluid Helium Invited Speaker: The Particle Image Velocimetry (PIV) technique has been expanded recently to the very low temperature environment to study the unique behavior of superfluid helium. Superfluid helium (He II) is a peculiar fluid with apparent zero viscosity and extraordinary heat transfer capabilities. The model that is traditionally used to explain this behavior considers He II to be made of two interpenetrating fluid components, one being viscous and the other being non-viscous. Recently, the PIV technique has been introduced to He II experimentation in an attempt to visualize the unique transport properties. As part of this effort, appropriate particles and seeding techniques have been developed for this low temperature fluid in order to measure the velocities of these internal flows. Initially, it was expected that the particles would track the viscous fluid component of He II, but several recent experiments have demonstrated their interaction with the non viscous fluid component as well. In order to fully benefit from the PIV technique to increase our knowledge and understanding of this unique fluid, the motion of the particles needs to be understood in terms of the motion of the two fluid components. An experiment combining heat transfer and forced flow allows one to independently vary these two component velocities and correlate them with the velocity of the seeded particles. In collaboration with Ernesto Bosque, Ting Xu, and Steven Van Sciver, NHMFL / Florida State University. [Preview Abstract] |
Sunday, November 23, 2008 11:58AM - 12:20PM |
BW.00005: Advances in Turbulence Studies Near T=0 Invited Speaker: Many advantages are beginning to be realized in the study of turbulence at cryogenic temperatures. However, the classic method of investigation, optical visualization, is increasingly difficult as the temperature of the test fluid is lowered toward absolute zero. In this presentation, the advantages of cryogenic fluid dynamic studies will be listed, and difficulties in realizing these methods will be listed as well. Many other details will be elucidated in the following presentations. Here, in particular, the extreme difficulties encountered very near absolute zero, where liquid helium has zero viscosity and almost zero heat capacity, will be discussed. Techniques for generating turbulence using rotation, vibration, and pulled grids will be explained. Visualization methods such as measuring local and global heating, and temperature and pressure fluctuations in sub-millimeter size fluid volumes, will be developed. Future exciting possibilities for untested methods of visualization will also be considered. [Preview Abstract] |
Sunday, November 23, 2008 12:20PM - 12:42PM |
BW.00006: Particle-Vortex Interaction in Superfluid Helium Invited Speaker: The application of the classical Particle Image Velocimetry (PIV) technique in liquid helium has opened the way to better visualization of superfluid turbulence. To interpret the data, it is necessary to understand the interaction between micron-size tracer particles and vortex lines. This talk summarizes current understanding of this interaction resulting from theoretical and numerical calculations. In collaboration with Yuri A. Sergeev, Newcastle University. [Preview Abstract] |
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