Superfluid turbulence in two-fluid flow of helium II

The completion of measurements of the dissipation for independently varied normal-fluid and superfluid velocities is presented. These measurements show the propagation of the first and second critical velocities into the (V sub n, V sub s) plane above the thermal counterflow line and provide a data base with which to compare theoretical predictions. The steady state dissipation delta T was measured across the ends of a flow tube (d = 134 micrometers) during laminar and turbulent flow. These flow states were produced using a combination of thermal counterflow procedures and using a very fine fiberglass bundle to produce a pure superflow via film flow of the superfluid component. These data show that the first critical velocity is actually a closed boundary separating laminar flow at small normal-fluid and superfluid velocities from turbulent flow at higher combinations. It was also found that the second critical velocity propagates into the (V sub n, V sub s) plane above thermal counterflow. The transition becomes increasingly abrupt as V sub n is increased. These two boundaries define three regions of turbulence in the (V sub n, V sub s) plane. The turbulence in regions for high V sub n appears to be homogeneous fitting a simple mutual friction model. The TI/TII Boundary separates this region from one of low-level dissipation. These flow states are very complicated and the dissipation here can oscillate between two values. The first critical velocity separates laminar flow states from a turbulent state obeying a modified mutual friction model suggested by Baehr and Tough. This type of turbulence exists both above and below the thermal counterflow line.