Quantum, or classical turbulence?

Our experimental answer is that in thermal counterflow of superfluid He-4 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 l(exp) straddling two orders of magnitude across the average distance l between quantized vortices. The Lagrangian dynamics of solid deuterium particles of size d approximate to l/10 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 l(exp) less than or similar to l, to the nearly Gaussian form typical of classical turbulent flows, at l(exp) greater than or similar to l. Copyright (C) EPLA, 2014