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Deformation and breakup of bubbles interacting with single vortex rings
International Journal of Multiphase Flow ( IF 3.8 ) Pub Date : 2021-06-22 , DOI: 10.1016/j.ijmultiphaseflow.2021.103734
F.J. Foronda-Trillo , J. Rodríguez-Rodríguez , C. Gutiérrez-Montes , C. Martínez-Bazán

The turbulent breakup of bubbles is a complex phenomenon present in a large number of engineering applications and natural processes. Simplified models are essential to better understand the interaction between turbulent eddies and bubbles. Probably the simplest one is that given by a vortex ring colliding with a single bubble. With this motivation, in the present work we perform three-dimensional numerical simulations of a single vortex ring of initial circulation Γ0, radius R0 and Reynolds number Re=Γ0/νl=15,000, interacting with a bubble of radius Rb immersed in a liquid of kinematic viscosity νl. The temporal evolution of the vortex ring is compared with analytical models for the size of the vortex core, a(t), the kinetic energy, Ek(t), and the enstrophy Ω(t), looking for a concurrence of this magnitude with the rate of dissipation of Ek. The dynamics of the bubble-vortex interaction process is described varying the vortex-to-bubble size ratio, R0/Rb, and the Weber number, We=ρl(Γ0/2πR0)2/(σ/Rb). With respect to the bubble, the simulations show that vortices smaller or of the same size as the bubble are not able to break it up. However, vortices slightly larger, although of comparable sizes, can efficiently break the bubble after trapping it inside the vortex core. In these cases, if the Weber number is sufficiently large, the bubble migrates to the vortex core, where the strain is maximum, and elongates along the azimuthal direction to eventually break by a Rayleigh-Plateau mechanism. In fact, we observe that the bubbles always break if We1 when R0/Rb>1. The numerical results are corroborated experimentally for vortex-to-bubble diameter ratios in the range 2.28R0/Rb7.5. Regarding the vortex ring, it is observed that when the vortex decelerates the bubble while they interact, the vorticity contained in the bubble boundary layer is engulfed by the vortex core, destabilizing the vortex ring. This makes the total enstrophy to suddenly increase due to the vorticity generation by the vortex stretching mechanism that follows the lost of axial symmetry. This increase in enstrophy is associated to a rapid decrease of kinetic energy, especially at low Weber numbers.



中文翻译:

气泡与单个涡环相互作用的变形和破裂

气泡的湍流破裂是大量工程应用和自然过程中存在的复杂现象。简化模型对于更好地理解湍流涡流和气泡之间的相互作用至关重要。最简单的可能是涡环与单个气泡碰撞所产生的。出于这个动机,在目前的工作中,我们对初始循环的单个涡环进行三维数值模拟Γ0, 半径 R。0 和雷诺数 R。电子=Γ0/ν=15日,000, 与半径气泡相互作用 R。 浸入具有运动粘度的液体中 ν. 将涡环的时间演化与涡核大小的分析模型进行比较,一种(),动能, E.(), 和内摄 Ω(), 寻找这个数量级与耗散率的一致性 E.. 气泡-涡流相互作用过程的动力学被描述为改变涡流与气泡的尺寸比,R。0/R。,和韦伯数, W。电子=ρ(Γ0/2πR。0)2/(σ/R。). 关于气泡,模拟表明较小或与气泡相同大小的涡流无法将其击碎。然而,稍大的涡流虽然大小相当,但在将其困在涡流中后可以有效地击碎气泡核。在这些情况下,如果韦伯数足够大,气泡会迁移到涡核,在那里应变最大,并沿方位角方向拉长,最终通过瑞利-高原机制破裂。事实上,我们观察到如果气泡总是破裂W。电子1 什么时候 R。0/R。>1. 数值结果通过实验证实了范围内的涡流与气泡直径比2.28R。0/R。7.5. 关于涡环,观察到当涡流在它们相互作用时使气泡减速时,气泡边界层中包含的涡量被涡核吞没,使涡环不稳定。由于轴对称性丧失后涡旋拉伸机制产生涡量,这使得总熵突然增加。这种熵的增加与动能的快速减少有关,尤其是在韦伯数较低的情况下。

更新日期:2021-07-04
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