可視化法によるHe II熱カウンター流ジェットの研究

抄録

A method of flow visualization in He II was developed by the use of H₂-D₂ solid particles and hollow glass spheres as tracers which were prepared to be neutral buoyant in He II. Streaks of tracers which follow the normal fluid flow enable us to see flow structure. It is of great importance in fluid dynamics to grasp a flow field as a pattern as well as to take a quantitative measurement.
The thermal counterflow jet was investigated by means of this method. A motor-driven 35-mm camera was used to photograph each flow event. Some pictures are examined to recognize flow patterns and others to measure the flow velocity from the lengths of particle streaks. The jet evolution appeared depending on the Reynolds number quite similarly to usual viscous fluids. The traceability was found to be satisfactory at least up to about 6cm/s for both kinds of tracers. The existence of large scale vortical structure in fully developed jets and the occurrence of wide-spread entrainment into main jet from the surroundings were evidently pointed out in the pictures. The calculation of the total momentum flux in jet indicates that the zero-relative-velocity situation is reached in the fully developed stage of turbulent jet.