NORMAL FLUID VELOCITY PROFILE AND TRANSITION FROM T-1 TO T-2 STATE OFSUPERFLUID TURBULENCE

It has been known for many years that in a circular counterflow pipe t here exist two different states of turbulence of helium II: the T-1 st ate, which appears at low valves of heat put, and the T-2 state, which appears suddenly at higher heat flux and is characterized by a much h igher density of quantized vortex lines. Until now the nature of the t wo turbulent states has been a mystery. To understand this problem we have addressed the issue of the velocity profile of the normal fluid a nd its stability. The computed critical heat flux Of the transition fr om the T-1 state to the T-2 state is found to be in good agreement wit h the observations. The result indicates that in the T-l state the sup erfluid is turbulent but the normal fluid is Still laminar. The T-1 to T-2 transition corresponds to the onset of normal fluid turbulence. P ACS numbers: 47.27, 47.37 and 67.40.