M. La Mantia

Quantum, or classical turbulence?

Our experimental answer is that in thermal counterflow of superfluid 4He both quantum and classical characteristics of turbulence can be detected simultaneously, depending on the length scale at which this quantum flow is probed. We study it at length scales straddling two orders of magnitude across the average distance l between quantized vortices. The Lagrangian dynamics of solid deuterium particles of size is investigated by using the particle tracking velocimetry technique. The normalized probability distribution of the particle velocity changes from the power-law shape typical of quantum turbulence, at scales , to the nearly Gaussian form typical of classical turbulent flows, at .

Particle dynamics in wall-bounded thermal counterflow of superfluid helium

The motions of relatively small particles in wall-bounded thermal counterflow of superfluid helium are experimentally investigated, above 1 K, by using the particle tracking velocimetry technique. The effect of a solid boundary on this quantum flow has received little attention to date, and the focus here is on the corresponding flow-induced particle dynamics. The velocity and velocity difference statistical distributions of the particles are computed at length scales straddling two orders of magnitude across the mean distance between quantized vortices, the quantum length scale of the flow. The imposed counterflow velocity ranges between about 2 and 7 mm/s, resulting in suitably defined Reynolds numbers up to 20 000. The distributions are found to be wider in the bulk than close to the solid boundary, at small enough scales, and this suggests that the mean distance between the vortices increases with the distance from the wall. The outcome reinforces the view, supported to date solely by numerical simula...