An experimental study of two identical air bubbles rising side-by-side in water

2021 
We experimentally study the dynamics of two identical air bubbles rising side-by-side in water by varying two parameters, namely, the radius of the bubble and center to center distance between them. The bubbles follow a three-dimensional spiraling motion, and their path and shape oscillations are observed in both the front and top views by using a high speed camera with a back-lit illumination and a mirror arrangement. Bubbles of different sizes are created by using a dumping cup mechanism, and the center to center distance between the two bubbles is varied by using telescopic joints. The dynamics of the two side-by-side bubbles is compared and contrasted with that of a single rising bubble. We found that the bubbles act independent of each other, like a single bubble, when the center to center distance is greater than seven times the radius of the bubbles. For similar separation distances, increasing the size of the bubbles results in a smaller terminal velocity and also lesser deviation from a spiral path due to high inertia.
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