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Exploration Of Thermal Counterflow In He Ii Using Particle Tracking Velocimetry

Title: Exploration Of Thermal Counterflow In He Ii Using Particle Tracking Velocimetry.
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Name(s): Mastracci, Brian, author
Guo, Wei, author
Type of Resource: text
Genre: Journal Article
Text
Journal Article
Date Issued: 2018-06-22
Physical Form: computer
online resource
Extent: 1 online resource
Language(s): English
Abstract/Description: Flow visualization using particle image velocimetry (PIV) and particularly particle tracking velocimetry (PTV) has been applied to thermal counterflow in He II for nearly two decades now, but the results remain difficult to interpret 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, in one early experiment it was observed (using PTV) that tracer particles move at the normal fluid velocity v(n), while in another it was observed (using PIV) that particles move at v(n)/2. Besides the different visualization methods, the range of applied heat flux investigated by these experiments differed by an order of magnitude. To resolve this apparent discrepancy and explore the statistics of particle motion in thermal counterflow, we apply the PTV method to a wide range of heat flux at a number of different fluid temperatures. In our analysis, we introduce a scheme for analyzing the velocity of particles presumably moving with the normal fluid separately from those presumably influenced by the quantized vortex tangle. Our results show that for lower heat flux there are two distinct peaks in the streamwise particle velocity probability density function (PDF), with one centered at the normal fluid velocity v(n) (named G2 for convenience) while the other is centered 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 quantitatively that there is no size difference between the particles contributing to G1 and G2. We also show that nonclassical features of the transverse particle velocity PDF arise entirely from G1, while the corresponding PDF for G2 exhibits the classical Gaussian form. The G2 transverse velocity fluctuation, backed up by second sound attenuation in decaying counterflow, suggests that large-scale turbulence in the normal fluid is absent from the two-peak region. We offer a brief discussion of the physical mechanisms that may be responsible for our observations, revealing that G1 velocity fluctuations may be linked to fluctuations of quantized vortex line velocity, and suggest a number of numerical simulations that may reveal the underlying physics in detail.
Identifier: FSU_libsubv1_wos_000436043200001 (IID), 10.1103/PhysRevFluids.3.063304 (DOI)
Keywords: superfluid he-4, visualization, dynamics, pressure, liquid-helium-ii, mutual friction, quantized vortices, quantum turbulence, reconnection, vortex
Publication Note: The publisher’s version of record is available at https://doi.org/10.1103/PhysRevFluids.3.063304
Persistent Link to This Record: http://purl.flvc.org/fsu/fd/FSU_libsubv1_wos_000436043200001
Owner Institution: FSU
Is Part Of: Physical Review Fluids.
2469-990X
Issue: iss. 6, vol. 3

Choose the citation style.
Mastracci, B., & Guo, W. (2018). Exploration Of Thermal Counterflow In He Ii Using Particle Tracking Velocimetry. Physical Review Fluids. Retrieved from http://purl.flvc.org/fsu/fd/FSU_libsubv1_wos_000436043200001