Study on Instabilities of Two-Phase He II/vapor flow in a pipe

本研究的目的是分析由超流体、正流体和气相组成的液氦多相流的流动不稳定性。对超流氦多相流生成实验装置进行了改进。为了实现高精度测量，对超流氦进行热屏蔽是非常重要的。为了保护液氦不受外界热量的影响，在上游和下游储罐以及试验段周围加了铜屏蔽。利用改进后的装置，在试验段产生了超流氦的两相流，得到了雷诺数与空化数的关系数据。因此，证实了空化数随着雷诺数的增加而减小。此外，还对这些现象进行了数值分析。假设两相流为气泡空化，建立了连续统方程、动量方程和能量守恒方程。用SMAC方法求解了这些方程，并分析了喷嘴处的流动结构。因此，在排气时，压力立即下降，并在喉部下游产生涡流。

The aim of this research is to analyze the flow instability of multi-phase flow of liquid helium which consists of superfluid, normalfluid and vapor phase.The experimental apparatus for the generation of multiphase flow of superfluid helium is improved. It is important to shield the superfliud helium from the heat for high accuracy measurement. To protect the liquid helium from the outside heat the copper shield is added to the upstream and downstream tank and around the test section. Using this improved apparatus, the two-phase flow of superfluid helium is generated at the test section and the data of the relation between Reynolds number and cavitation number are obtained. For this reason, it is confirmed that the cavitation number is decreased as the Reynolds number is increased.Moreover, the phenomena are analyzed by the numerical method. The two-phase flow is assumed as bubble cavitation and the governing equations are constructed so that continuum equation, momentum equation and energy conservation is satisfied. These equations are solved by SMAC method and the flow structure at the nozzle is analyzed. Consequently, at the blowdown, the pressure decreases immediately and vortex is generated downstream of the throat.