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On the Transition from Potential Flow to Turbulence Around a Microsphere Oscillating in Superfluid 4He

  • The flow of superfluid around a translationally oscillating sphere, levitating without mechanical support, can either be laminar or turbulent, depending on the velocity amplitude. Below a critical velocity that scales as and is temperature independent below 1 K, the flow is laminar (potential flow). Below 0.5 K, the linear drag force is caused by ballistic phonon scattering that vanishes as until background damping, measured in the empty cell, becomes dominant for K. Increasing the velocity amplitude above leads to a transition from potential flow to turbulence, where the large turbulent drag force varies as . In a small velocity interval % above , the flow is unstable below 0.5 K, switching intermittently between both patterns. From time series recorded at constant temperature and driving force, the lifetimes of both phases are analyzed statistically. We observe metastable states of potential flow which, after a mean lifetime of 25 min, ultimately break down due to vorticity created by natural background radioactivity. The lifetimes of the turbulent phases have an exponential distribution, and the mean increases exponentially with . We investigate the frequency at which the vortex rings are shed from the sphere. Our results are compared with recent data of other authors on vortex shedding by moving a laser beam through a Bose-Einstein condensate. Finally, we show that our observed transition to turbulence belongs to the class of "supertransient chaos" where lifetimes of the turbulent states increase faster than exponentially.

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Metadaten
Author:Michael NiemetzORCiDGND, Risto HänninenORCiD, Wilfried SchoepeORCiD
DOI:https://doi.org/10.1007/s10909-017-1745-7
Parent Title (English):Journal of low temperature physics
Publisher:Springer Nature
Document Type:Article
Language:English
Year of first Publication:2017
Release Date:2022/05/12
Tag:Bose-Einstein condensates; Critical velocity; DYNAMICS; EINSTEIN CONDENSED GAS; HE-4; HELIUM; LAMINAR; MK TEMPERATURES; ONSET; Oscillatory flow; Quantum turbulence; Superfluid helium; Vortex shedding
Volume:187
Issue:3-4
First Page:195
Last Page:220
Institutes:Fakultät Elektro- und Informationstechnik
Fakultät Elektro- und Informationstechnik / Labor Datenkommunikation
Begutachtungsstatus:peer-reviewed
research focus:Energie und Mobilität
Licence (German):Keine Lizenz - Es gilt das deutsche Urheberrecht: § 53 UrhG