弹状泡是一种在自然界和工业生产中常见的气液两相流现象。尽管已经有大量的研究聚焦于竖直圆管中自由上浮的弹状泡的运动，但是对于它们在扩张管道中的行为，我们仍然知之甚少。当弹状泡进入扩张管道时，它们会经历复杂的动态变化，这可能导致气泡变形甚至断裂，从而导致压力波动和射流形成。本研究设计了一个实验装置，进行了不同长度的气泡在进入具有不同管道直径，液体粘度和扩张角度的扩张段的实验，系统性研究了自由上升的弹状泡进入竖直管道扩张段时的动态行为。本研究首先探究了自由上升的弹状泡从竖直圆管直接进入自由水域时产生的动态行为。通过实验，我们发现弹状泡的颈缩过程满足幂律，该幂律受无量纲数控制，幂律指数越高，颈缩过程就越快，夹断时间就越短。弹状泡颈部上方的形状变化与颈缩过程密切相关，影响气泡断裂所需的临界气体体积。本文还发现了两种射流形成机理：一种是在气泡未发生夹断时，由气泡尾部周围液体尾流的变形和加速引起的，这一射流速度会随着气泡体积的增大而增大，另一种是在气泡发生夹断时，由液体流动在气泡颈部的汇聚撞击引起的，其射流速度会随着气泡体积的增大而减小，并且探究了这两种不同规律的内在机理。在此基础上，本研究了引入不同扩张角度的扩张流道，探究扩张角度对于气泡和射流的动力学行为的影响。实验发现，扩张角度会显著影响气泡的颈缩过程，从而影响临界气体体积。扩张角对于气泡颈缩过程的影响也显著影响到了两种不同射流的速度规律，对于气泡夹断时形成的射流，发现当夹断点下方气泡体积一样时，角度更小的扩张管道会形成更加快速的射流，同时由于扩张角度对于临界气泡体积的影响，大气泡更容易在小扩张角的扩张管道中产生集中且快速的射流。这些发现为后续更加深入的研究这一过程中的打好了基础，为后续的研究提供了新的思路和方向，有可能可以为火山和间歇泉等喷发现象的机理提供新的视角和解释。在未来的研究中，我们可以进一步探究气泡在不同液体中的扩张行为，以及不同形状和大小的管道对于气泡行为的影响等问题。
Taylor bubbles are a common gas-liquid two-phase flow phenomenon found in both nature and industrial production. Although a considerable amount of research has focused on the movement of freely rising Taylor bubbles in vertical circular tubes, little is known about their behavior in expanding pipes. As Taylor bubbles enter expanding pipes, they undergo complex dynamic changes, potentially leading to bubble deformation or even rupture, causing pressure fluctuations and jet formation. In this study, an experimental setup was designed to investigate the dynamics of Taylor bubbles of varying lengths entering expansion sections with different pipe diameters, liquid viscosities, and expansion angles.First, the dynamics of freely rising Taylor bubbles entering open water directly from a vertical circular pipe were explored. Through experiments, it was discovered that the neck contraction process of Taylor bubbles follows a power-law, which is controlled by dimensionless numbers. A higher power-law exponent indicates a faster neck contraction process and a shorter pinch-off time. The shape changes above the neck of the Taylor bubble were found to be closely related to the neck contraction process, affecting the critical gas volume required for bubble rupture. Two mechanisms of jet formation were also identified: one occurring without pinch-off, caused by the deformation and acceleration of the liquid wake surrounding the bubble tail, where the jet velocity increases with the increase in bubble volume? and the other occurring during pinch-off, caused by the collision of liquid flow converging at the bubble neck, where the jet velocity decreases with increasing bubble volume. The underlying mechanisms of these two distinct patterns were investigated as well.Building on this foundation, expansion channels with different expansion angles were introduced to examine the impact of expansion angles on the dynamics of bubbles and jets. Experiments revealed that expansion angles significantly affect the neck contraction process of bubbles, subsequently influencing the critical gas volume. Expansion angles were also found to substantially impact the velocity patterns of the two different jets. For jets formed during bubble pinch-off, it was observed that smaller expansion angles generate faster jets when the volume of the bubble beneath the pinch-off point is the same. Furthermore, due to the effect of expansion angles on the critical bubble volume larger bubbles were more likely to generate concentrated and rapid jets in expansion pipeswith smaller angles.These findings laid the foundation for further in-depth investigations of this process, providing new insights and directions for subsequent research. The results may offer a new perspective and explanation for the mechanisms of eruptive phenomena such as volcanoes and geysers. In future studies, the expansion behavior of bubbles in different liquids can be further investigated, as well as the influence of various pipe shapes and sizes on bubble behavior.
