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Journal of Low Temperature Physics

, Volume 178, Issue 5–6, pp 383–391 | Cite as

Breakdown of Potential Flow to Turbulence Around a Sphere Oscillating in Superfluid \(^4\)He Above the Critical Velocity

  • W. Schoepe
  • R. Hänninen
  • M. Niemetz
Article

Abstract

The onset of turbulent flow around an oscillating sphere in superfluid \(^4\)He is known to occur at a critical velocity \(v_{\text {c}} \,\sim \sqrt{\kappa \,\omega }\) where \(\kappa \) is the circulation quantum and \(\omega \) is the oscillation frequency. But it is also well known that initially in a first up-sweep of the oscillation amplitude, \(v_{\text {c}}\) can be considerably exceeded before the transition occurs, thus leading to a strong hysteresis in the velocity sweeps. The velocity amplitude \(v_{\text {c}}^* > v_{\text {c}}\) where the transition finally occurs is related to the density \(L_0\) of the remanent vortices in the superfluid. Moreover, at temperatures below ca. 0.5 K and in a small interval of velocity amplitudes between \(v_{\text {c}}\) and a velocity that is about 2 % larger, the flow pattern is found to be unstable, switching intermittently between potential flow and turbulence. From time series recorded at constant temperature and driving force, the distribution of the excess velocities \(\Delta v = v_{\text {c}}^* - v_{\text {c}}\) is obtained and from that the failure rate. Below 0.1 K we also can determine the distribution of the lifetimes of the phases of potential flow. Finally, the frequency dependence of these results is discussed.

Keywords

Quantum turbulence Oscillatory flow Intermittent switching Remanent vorticity 

Notes

Acknowledgments

We are grateful to Jan Jäger and Hubert Kerscher for their co-operation. W.S. acknowledges discussions with Matti Krusius (Aalto University, Finland) and Shaun Fisher (Lancaster University, UK). R.H is supported by the Academy of Finland.

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Copyright information

© Springer Science+Business Media New York 2014

Authors and Affiliations

  1. 1.Fakultät für PhysikUniversität RegensburgRegensburgGermany
  2. 2.Low Temperature Laboratory, O.V. Lounasmaa LaboratoryAalto UniversityAaltoFinland
  3. 3.OTH RegensburgRegensburgGermany

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