Abstract
Quantum turbulence in thermal counterflow of superfluid 4 He is visualized and studied at length scales comparable to the average distance between quantized vortices. The lagrangian velocities of micrometer- sized deuterium particles are obtained in a planar section of the flow field by using the particle tracking velocime- try technique. It is shown that the lagrangian velocity normalized distributions are strongly non-gaussian, with power-law tails, in contrast to the nearly gaussian distributions obtained in classical turbulent flows. The average distance between quantized vortices can therefore be seen as the length scale indicating the transition between classical-like and quantum behavior in thermal counterflow of superfluid 4 He.
Highlights
Quantum turbulence, a fast developing field of research combining low temperature physics and fluid dynamics, can loosely be defined as the most general form of motion of quantum fluids displaying superfluidity, e.g., see [1] and [2]
It is shown that the lagrangian velocity normalized distributions are strongly non-gaussian, with power-law tails, in contrast to the nearly gaussian distributions obtained in classical turbulent flows
It clearly distinguishes quantum flows from classical turbulent flows, which are usually characterized by nearly gaussian velocity distributions
Summary
A fast developing field of research combining low temperature physics and fluid dynamics, can loosely be defined as the most general form of motion of quantum fluids displaying superfluidity, e.g., see [1] and [2]. If the temperature decreases further, liquid helium undergoes a second order phase transition and changes dramatically its properties It is called He II or superfluid 4He and its viscosity can be considered null at 0 K, i.e., the fluid is assumed inviscid in the zero-temperature limit and its behavior cannot be accounted for by using the Navier-Stokes equation, as if it were a classical viscous fluid. In other words, quantized vortices, i.e., line singularities where the superfluid density is null, can exist in superfluid helium These vortices usually arrange themselves in a tangle and the dynamical behavior of such a tangle constitutes an essential ingredient of quantum turbulence. In order to fulfill such a need, a novel experimental apparatus has been devised in our Prague low temperature laboratory [10] and corresponding results, recently obtained in thermal counterflow, are reported and discussed here
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