Quantum turbulence: Drag coefficient for oscillations of a quartz tuning fork immersed in He II

Experimental data on the motion of He II driven by an oscillating quartz tuning fork are analyzed. It is found that before a certain threshold of a parameter with the structure of the Reynolds number is reached, the normal and superfluid components move independently. Then the force and drag coefficient are entirely determined by the motion of the normal component. For values of the parameter above the threshold (critical for the velocity), turbulence sets in and is related to quantum effects below the superconducting transition temperature. The universality of the motion of liquid helium at temperatures above the transition point is also discussed. (C) 2015 AIP Publishing LLC.