Turbulence in boundary flow of superfluid 4He triggered by free vortex rings
This research is the collaboration between Elementary Excitation Physics Labo. and Ultra Low Temperature Labo.
The transition to turbulence in the boundary flow of superfluid 4He is investigated using a vortex--free vibrating wire. At high wire vibration velocities, we found that stable alternating flow around the wire enters a turbulent phase triggered by free vortex rings. Numerical simulations of vortex dynamics demonstrate that vortex rings can attach to the surface of an oscillating obstacle and expand unstably due to the boundary flow of the superfluid, forming turbulence. Experimental investigations indicate that the turbulent phase continues even after stopping the injection of vortex rings, which is also confirmed by the simulations.
Figures : As increasing the velocity of sphere (wire for the case of experiments), the system develops from non-turbulent (left) to turbulent (right) state.
R. Goto, S. Fujiyama, H. Yano, Y. Nago, N. Hashimoto, K. Obara, O. Ishikawa, M. Tsubota, and T. Hata, Phys. Rev. Lett. 100, 045301.