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

本研究的目的是从实验和理论上研究过饱和低温两相流的不稳定性。这一分析对火箭发动机涡轮泵等低温设备的改进具有一定的参考价值。空化模型采用漂移流模型，并采用轴对称系统。考虑了相变的影响。结果表明，相变对低温流体流场的影响表现为对喷嘴喉部下游尾涡中心含气率增加的抑制作用。此外，还证实了随着喷嘴喉部下游尾涡的发展，喷管壁面会产生逆流。接下来，对过饱和低温流体的两相流动进行了可视化实验。得到了不稳定流和稳定流的数据。结果表明，饱和状态下的空化流动较为稳定，并观察到气泡的连续产生。相反，过饱和状态下的空化流动非常不稳定，可以观察到任意气泡的产生。

The aim of this research is to investigate the instability of supersaturated cryogenic two-phase flow experimentally and theoretically. This analysis is useful to the improvement of cryogenic apparatus such as turbopumps of rocket engine.In this year numerical simulations are performed about the two-phase flow in the nozzle. The drift-flux model is used as the cavitation model and axisymmetric system is also used. The phase change is considered. As the results, the effect of phase change on flow field of cryogenic fluid appears the suppression of the increase of void fraction at the center of wake vortex generated downstream of nozzle throat. Moreover, it is confirmed that the counter flow generates at the wall of the nozzle as the wake vortex downstream of the nozzle throat grows up.Next, experiments are performed about the visualization of two-phase flow of supersaturated cryogenic fluid. The data of both instability flow and stability one are obtained. As the results, the cavitating flow at saturated state is comparatively stable and the successive generation of bubble is observed. On the contrary, the cavitating flow at supersaturated state is very unstable and arbitrary generation of bubble is observed.