An exploration of thermal counterflow in He II using particle tracking velocimetry

Abstract

Visualization of thermal counterflow in He II using PIV (particle image velocimetry) and PTV (particle tracking velocimetry) is difficult because tracer particle motion can be influenced by both the normal fluid and superfluid components of He II as well as the quantized vortex tangle. For instance, an early PTV experiment observed particles moving at the normal fluid velocity $v_n$, while a PIV experiment observed particles moving at $v_n/2$, though the range of heat flux applied in these experiments differed by an order of magnitude. To resolve this apparent discrepancy and explore statistics of particle motion in thermal counterflow, we have applied PTV to a wide range of heat flux at several fluid temperatures. We introduce a scheme for analyzing the velocity of particles presumably moving with the normal fluid separately from those presumably influenced by the vortex tangle. Our results show two distinct peaks in the streamwise particle velocity PDF (probability density function) for lower heat flux, one centered at the normal fluid velocity $v_n$ ("G2") and one near $v_n/2$ ("G1"). For higher heat flux there is a single peak centered near $v_n/2$ ("G3"). Using our separation scheme we show there is no size difference between particles contributing to G1 and G2. We also show that non-classical features of the transverse velocity PDF arise entirely from G1, while the corresponding PDF for G2 exhibits classical Gaussian form. G2 transverse velocity fluctuation, backed up by second sound attenuation in decaying counterflow, suggests large scale turbulence in the normal fluid is absent from the two peak region. We offer a brief discussion of physical mechanisms that may be responsible for our observations, revealing that G1 velocity fluctuations may be linked to fluctuations of vortex line velocity, and suggest numerical simulations that may reveal underlying physics in detail.

27 pages, 7 figures, submitted to Physical Review Fluids (currently under review)

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Cited by in corpus (13)

• Fully Coupled Two-Fluid Dynamics in Superfluid ${}^4$He: Anomalous Anisotropic Velocity Fluctuations in Counterflow
• Superdiffusion of quantized vortices uncovering scaling behavior of quantum turbulence
• Characterizing vortex tangle properties in steady-state He II counterflow using particle tracking velocimetry
• Eulerian and Lagrangian second-order statistics of superfluid ${}^4$He grid turbulence
• Molecular Tagging Velocimetry in Superfluid Helium-4: Progress, Issues, and Future Development
• Boiling and cavitation caused by transient heat transfer in superfluid helium-4
• Multi-scale energy budget of inertially driven turbulence in normal and superfluid helium
• Coupled dynamics of quantized vortices and normal fluid in superfluid ${}^4$He based on lattice Boltzmann method
• Dynamics of turbulent plugs in a superfluid ${}^4$He channel counterflow
• Vinen's latest thoughts on the "bump'' puzzle in decaying He II counterflow turbulence
• Hydrodynamic Decay of Decorated Quantum Vortex Rings
• Toy Model for Vortex Ring-Assisted Particle Drag in Superfluid Counterflow
• Studies on quantum turbulence with Vinen