Experimental Study on the Transition to Superfluid Turbulent Flow

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Several experimental approaches are attempted for the study of the transition of superfluid flow to superfluid tubulent flow, and the following results are obtained.i) Measurement of the thermal counterflow jet by applying a flow visualization tecnique and with a laser Doppler velocimeter : In particular, thermally excited 2nd sound Helmholtz oscillation is investigated to elusidate the condition for the appearance of the oscillation phenomena and to analyze the modulation to the oscillation as a result of the transition to the superfluid turbulent flow. The experimental results are found to agree with the prediction by the linear stability analysis. This fact seems to indicate that the Gorter-Mellink mutual friction term is a satisfactory approximation for the cases of small and slow disturbances.ii) Numerical simulation for the two-fluid equations (analysis of a thermal shock wave) : The effects of the introduction of the Gorter-Mellink term and of the equation of vortex density evol … More ution to the governing equations, both of which are phenomenological description for the interaction of the tangled vortices with a shock wave, are compared to see the wave form modification caused by the mutual friction. The comparison suggests that the latter treatment provides far better result but both approaches are still insufficient for a quantitative estimation.iii) Measurement of the flow through a fountain effect pump element in the superfluid turbulent flow (non-linear) region : It is indicated that the interior structure of an element should be taken into account to describe flow phenomena. A computer program on the basis of the flow model taking account of the interior structure is completed to predict the pump performance and the maximum flow rate.iv) Application of the laser hologram interferometry to superfluid measurement : The construction of the experimental apparatus including a cryostat with optical windows is nearly completed, and a preliminary experiment is successfully made. Experiment of a thermal shock wave in He II will be soon started to study the generation of tangled vortices behind a strong thermal shock wave and thus the transition of the He II field to the superfluid turbulent state. An Au-Sn superconducting thin film temperature detector for the thermal shock wave detection is manufactured and tested. Less