How critical is bubble size in vortex-bubble interaction: In connection with bubbly turbulent flows

What is it about?

We have studied the interaction of an air bubble with a vortical structure, namely, a (water) vortex ring, while the bubble is inside the ring. The focus is on the effects of the bubble-to-vortex size ratio on both the bubble dynamics and vortex ring dynamics. On the bubble side, its deformation and breakup dynamics are characterized by different regimes of the size ratios and the Weber numbers. Simultaneously, several features related to the spatio-temporal dynamics of the vortex ring, such as the ring growth, deformations, propagation, and azimuthal vorticity, are reported.

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Photo by Nancy Hughes on Unsplash

Photo by Nancy Hughes on Unsplash

Why is it important?

Bubbly turbulent flows are seen in numerous engineering and environmental applications, for example, chemical reactors, ocean surfaces, and drag reductions using bubbles in a water boundary layer. In these flows, bubbles are preferentially concentrated within the high vortical regions, and hence, to understand these flows, it would be essential to characterize bubble deformation/breakup inside these vortices, and, simultaneously, the bubble(s) induced modifications in the vortices, both of which are generally dependent on the Weber number. Such flows involve the interaction between multiple bubbles and vortices, making these complex to understand. Here, we study a simplified version of this, namely the interaction of a single bubble with a vortex ring, helping us understand and model these complex flows. The present work shows that the Weber number is generally sufficient to characterize some important quantities like the scaling for the size of broken bubbles after the interaction relatively independent of the bubble size. However, the effect that the bubble has on the vortex is shown to be critically dependent on the bubble size with respect to the vortex core, even at a fixed Weber number.

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