Velocity Statistics in Quantum Turbulence

AbstractQuantum turbulence in thermal counterflow of superfluid 4He is studied at length scales comparable to the average distance R between quantized vortices. The Lagrangian velocities of micrometer-sized deuterium particles, smaller here than R, are calculated in a planar section of the experimental volume by using the particle tracking velocimetry technique. It is confirmed 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 probability density functions of the velocity differences along the particle trajectories, that is, the Lagrangian velocity structure functions of order 1, are also computed. Their shape changes from a strongly non-Gaussian form to a nearly Gaussian one as the corresponding Lagrangian time delay increases, showing thus an unexpected classical-like behavior