Thermal Counterflow Of Superfluid Research Articles

Ubiquity of particle–vortex interactions in turbulent counterflow of superfluid helium

Abstract

Numerical Study on Entrance Length in Thermal Counterflow of Superfluid $$^4$$He

Three-dimensional numerical simulations in a square duct were conducted to investigate entrance lengths of normal fluid and superfluid flows in a thermal counterflow of superfluid $^4$He. The two fluids were coarse-grained by using the Hall-Vinen-Bekharevich-Khalatnikov (HVBK) model and were coupled through mutual friction. We solved the HVBK equations by parameterizing the coefficient of the mutual friction to consider the vortex line density. A uniform mutual friction parameter was assumed in the streamwise direction. Our simulation showed that the entrance length of the normal fluid from a hot end becomes shorter than that of a single normal fluid due to the mutual friction with the parabolically developed superfluid flow near the hot end. As the mutual friction increases, the entrance length decreases. Same as that, the entrance length of the superfluid from a cold end is affected by the strength of the mutual friction due to the parabolically developed normal fluid flow near the cold end. Aside from the entrance effect, the realized condition of a tail-flattened flow is discussed by parameterizing the superfluid turbulent eddy viscosity and the mutual friction.

Lagrangian velocity distributions in thermal counterflow of superfluid4He

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.