Breakdown of Potential Flow to Turbulence Around a Sphere Oscillating in Superfluid $$^4$$4He Above the Critical Velocity
Breakdown of Potential Flow to Turbulence Around a Sphere Oscillating in Superfluid $$^4$$4He Above the Critical Velocity
复制标题
超流体中振荡球体周围湍流的势流分解 $$^4$$4He 高于临界速度
DOI：
--
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发表时间：
2014
期刊：
影响因子：
--
通讯作者：
M. Niemetz
中科院分区：
文献类型：
--
作者：
W. Schoepe;R. Hänninen;M. Niemetz
The onset of turbulent flow around an oscillating sphere in superfluid $$^4$$4He is known to occur at a critical velocity $$v_{ ext {c}} ,sim sqrt{kappa ,omega }$$vc∼κω where $$kappa $$κ is the circulation quantum and $$omega $$ω is the oscillation frequency. But it is also well known that initially in a first up-sweep of the oscillation amplitude, $$v_{ ext {c}}$$vc can be considerably exceeded before the transition occurs, thus leading to a strong hysteresis in the velocity sweeps. The velocity amplitude $$v_{ ext {c}}^* > v_{ ext {c}}$$vc∗>vc where the transition finally occurs is related to the density $$L_0$$L0 of the remanent vortices in the superfluid. Moreover, at temperatures below ca. 0.5 K and in a small interval of velocity amplitudes between $$v_{ ext {c}}$$vc 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 $$Delta v = v_{ ext {c}}^* - v_{ ext {c}}$$Δv=vc∗-vc 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.
The onset of turbulent flow around an oscillating sphere in superfluid $$^4$$4He is known to occur at a critical velocity $$v_{ ext {c}} ,sim sqrt{kappa ,omega }$$vc∼κω where $$kappa $$κ is the circulation quantum and $$omega $$ω is the oscillation frequency. But it is also well known that initially in a first up-sweep of the oscillation amplitude, $$v_{ ext {c}}$$vc can be considerably exceeded before the transition occurs, thus leading to a strong hysteresis in the velocity sweeps. The velocity amplitude $$v_{ ext {c}}^* > v_{ ext {c}}$$vc∗>vc where the transition finally occurs is related to the density $$L_0$$L0 of the remanent vortices in the superfluid. Moreover, at temperatures below ca. 0.5 K and in a small interval of velocity amplitudes between $$v_{ ext {c}}$$vc 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 $$Delta v = v_{ ext {c}}^* - v_{ ext {c}}$$Δv=vc∗-vc 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.
超流体 4He 中石英音叉的迟滞、切换和异常行为
影响因子：
2
作者：
Bradley D
通讯作者：
Bradley D