Transition to superfluid turbulence in two-fluid flow of He II

Abstract

We have extended our previous measurements of the transition to superfluid turbulence in flows where the superfluid and normal-fluid velocities can be varied independently. The results indicate that the critical line in the $V_n$-$V_s$ plane which forms the boundary between laminar flow and superfluid turbulence is a closed curve about the origin. The existence of this critical line suggests that most theories of the critical velocity in He II are incomplete.