We present an exploratory study of the hydrodynamical interaction between two bubbles rising at high Reynolds numbers in a thin-gap cell. When they are isolated, the bubbles exhibit oscillatory motions and develop an unsteady wake with periodic release of vortices. Experiments combine bubble tracking and measurements of the liquid velocity field through volumetric time-resolved particle image velocimetry. This enabled us to analyse the kinematics of the bubbles during their interaction in relationship with the liquid flow field induced by their motion and governing their behaviour. We first investigate how the kinematics of a bubble, already submitted to the intrinsic instability of its path and wake, is modified by the interaction, i.e. by the presence of a liquid flow field generated by the companion bubble. Two main effects are highlighted in association with (i) the role of the ascending flow generated by the leading bubble, and of its spatial evolution, leading to a slowly varying vertical entrainment of the trailing bubble, and (ii) the role of the vortices released by the leading bubble inducing strong localized horizontal deviations on a bubble in line or in oblique positioning. In the latter case, two major scenarios are identified: deviations of the trailing bubble towards the wake centre line (centring in the wake) or away from it (ejection from the wake). We also show that a regular succession of ejections and re-alignments events may take place (cyclic alternation of ejections and centrings). The analysis is built on the knowledge of the behaviour of isolated bubbles, which is used as the basis for comparison to characterize the effect of the interaction, for the modelling of the vertical entrainment, and for the definition of a criteria on a dimensionless parameter characterizing the ability of a vortex to drive the bubble motion. In turn, we investigate the effect of a bubble passage in the liquid flow field generated by the companion bubble, highlighting the destruction or reinforcement of vortices. We show in particular that both effects can occur without a significant impact on the bubble kinematics.

中文翻译：

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在薄间隙单元中上升的两个振荡气泡的相互作用：垂直夹带和与涡旋的相互作用

我们对薄间隙电池中以高雷诺数上升的两个气泡之间的流体动力学相互作用进行了探索性研究。当它们被隔离时，气泡表现出振荡运动，并随着涡流的周期性释放而形成不稳定的尾流。实验通过体积时间分辨粒子图像测速法将气泡跟踪和液体速度场的测量结合起来。这使我们能够分析气泡在与由其运动引起的液体流场相互作用并控制其行为的过程中的运动学。我们首先研究已经受到其路径和尾流固有不稳定性影响的气泡的运动学如何通过相互作用进行修改，即通过伴随气泡产生的液体流场的存在。突出显示了两个主要影响与 (i) 领先气泡产生的上升流的作用及其空间演变，导致尾随气泡的垂直夹带缓慢变化，以及 (ii) 涡旋的作用由前导气泡释放，在直线或倾斜定位的气泡上引起强烈的局部水平偏差。在后一种情况下，确定了两种主要情况：尾随气泡朝向尾流中心线（以尾流为中心）或远离中心线（从尾流中弹出）的偏差。我们还表明，可能会发生定期连续的弹射和重新对齐事件（弹射和中心的循环交替）。该分析建立在对孤立气泡行为的了解之上，它被用作比较的基础来表征相互作用的影响，垂直夹带的建模，以及定义描述涡流驱动气泡运动能力的无量纲参数的标准。反过来，我们研究了气泡通道在伴随气泡产生的液体流场中的影响，突出了涡流的破坏或增强。我们特别表明，这两种效应都可以发生，而不会对气泡运动学产生重大影响。强调涡旋的破坏或加强。我们特别表明，这两种效应都可以发生，而不会对气泡运动学产生重大影响。强调涡旋的破坏或加强。我们特别表明，这两种效应都可以发生，而不会对气泡运动学产生重大影响。