QFS2016 Book of Abstracts

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. 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. We acknowledge the support of Charles University under GAUK grant no. 1109416.

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