The emphasis of this review is to discuss three peculiar phenomena of bubbles rising in viscoelastic fluids, namely, the formation of a cusp, negative wake, and velocity jump discontinuity, and to highlight the possible future directions of the subject. The mechanism and influencing factors of these three peculiar phenomena have been discussed in detail in this review. The evolution of the bubble shape is mainly related to the viscoelasticity of the fluid. However, the mechanisms of the two-dimensional cusp, tip-streaming, “blade-edge” tip, “fish-bone” tip, and the phenomenon of the tail breaking into two different threads, in some special viscoelastic fluids, are not understood clearly. The origin of the negative wake behind the bubbles rising in a viscoelastic fluid can be attributed to the synergistic effect of the liquid-phase viscoelasticity, and the bubbles are large enough; thus, leading to a very long relaxation time taken by the viscoelastic stresses. For the phenomenon of bubble velocity jump discontinuity, viscoelasticity is the most critical factor, and the cusp of the bubbles and the surface modifications play only ancillary roles. It has also been observed that a negative wake does not cause velocity jump discontinuity.

中文翻译：

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粘弹性液体中单气泡运动特性上升的综述

这篇综述的重点是讨论粘弹性流体中气泡上升的三种特殊现象，即尖点的形成、负尾流和速度跳跃不连续性，并强调该课题未来可能的发展方向。本综述详细讨论了这三种特殊现象的发生机制和影响因素。气泡形状的演变主要与流体的粘弹性有关。然而，在一些特殊的粘弹性流体中，二维尖端、尖端流动、“刀刃”尖端、“鱼骨”尖端以及尾部断裂成两条不同线的现象的机制尚不清楚清楚地。粘弹性流体中气泡上升背后的负尾流的起源可归因于液相粘弹性的协同作用，而且气泡够大；因此，导致粘弹性应力需要很长的松弛时间。对于气泡速度跳跃不连续现象，粘弹性是最关键的因素，气泡的尖端和表面改性只起辅助作用。还观察到负尾流不会导致速度跳跃不连续。