Analysis of motion of solid hydrogen tracer particles in oscillating superfluid flows

27th International Conference on Low Temperature Physics

Zemma, E.^1,2 ; Luzuriaga, J.^1 ; Babuin, S.^3

Centro Atómico Bariloche, CNEA, Inst. Balseiro UNC, S.C. Bariloche

8400, Argentina^1

CONICET, Argentina^2

Institute of Physics ASCR, Na Slovance 2, Praha 8

182 21, Czech Republic^3

关键词: Distribution of velocity;    Exponential decays;    Frames per seconds;    Logarithmic decay;    Low velocities;    Particle tracking velocimetry;    Superfluid flows;    Tracer particle;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/568/1/012029/pdf
DOI  :  10.1088/1742-6596/568/1/012029

来源: IOP

【 摘 要 】

We have developed a relatively simple cryostat which allows us to image turbulent flows in superfluid helium at temperatures below 2 K, using frozen H2 particles. We analyze the statistics of the velocities of these solid tracers, which follow the turbulent flow generated by oscillating bodies. We have also studied one of the oscillators working in air at room temperature, and traced the flow with solid talcum particles for comparison. Images were recorded by a digital camera at 240 frames per second, while frequencies of the oscillators are between 20 to 45 Hz. The flow is characterized by a modified Reynolds number Reδbased on the viscous penetration depth δ. Software in a dedicated particle tracking velocimetry code allows us to compute the trajectories and velocities of tens of thousands of particles. We have obtained the number of particles for equally spaced intervals of the velocity modulus. For the oscillators in the superfluid, the probability of finding particles at higher velocities has an exponential decay. Within our resolution the statistics in the superfluid for oscillating objects with sharp borders is largely independent of Reδ, while the logarithmic decay at low velocities seems faster than for high velocities for rounded objects. On the other hand, for data taken in air the result is closer to a classical Gaussian distribution of velocities.