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Title: Second-sound studies of coflow and counterflow of superfluid {sup 4}He in channels

We report a comprehensive study of turbulent superfluid {sup 4}He flow through a channel of square cross section. We study for the first time two distinct flow configurations with the same apparatus: coflow (normal and superfluid components move in the same direction), and counterflow (normal and superfluid components move in opposite directions). We realise also a variation of counterflow with the same relative velocity, but where the superfluid component moves while there is no net flow of the normal component through the channel, i.e., pure superflow. We use the second-sound attenuation technique to measure the density of quantised vortex lines in the temperature range 1.2 K ≲ T ≲ T{sub λ} ≈ 2.18 K and for flow velocities from about 1 mm/s up to almost 1 m/s in fully developed turbulence. We find that both the steady-state and temporal decay of the turbulence significantly differ in the three flow configurations, yielding an interesting insight into two-fluid hydrodynamics. In both pure superflow and counterflow, the same scaling of vortex line density with counterflow velocity is observed, L∝V{sub cf}{sup 2}, with a pronounced temperature dependence; in coflow instead, the vortex line density scales with velocity as L ∝ V{sup 3/2} and ismore » temperature independent; we provide theoretical explanations for these observations. Further, we develop a new promising technique to use different second-sound resonant modes to probe the spatial distribution of quantised vortices in the direction perpendicular to the flow. Preliminary measurements indicate that coflow is less homogeneous than counterflow/superflow, with a denser concentration of vortices between the centre of the channel and its walls.« less
Authors:
;  [1] ;  [2]
  1. Faculty of Mathematics and Physics, Charles University, Ke Karlovu 3, 12116 Prague (Czech Republic)
  2. Institute of Physics ASCR, Na Slovance 2, 180 00 Prague (Czech Republic)
Publication Date:
OSTI Identifier:
22403237
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Fluids (1994); Journal Volume: 27; Journal Issue: 6; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 42 ENGINEERING; CONCENTRATION RATIO; COUNTERFLOW SYSTEMS; DENSITY; FLOW RATE; FLUIDS; HELIUM 4; HYDRODYNAMICS; SECOND SOUND; SPATIAL DISTRIBUTION; STEADY-STATE CONDITIONS; SUPERFLUIDITY; TEMPERATURE DEPENDENCE; TEMPERATURE RANGE; TURBULENCE; VORTICES