Backflipping motion of air bubbles colliding with a tilted wall

TL;DR

This study investigates the backflipping motion of air bubbles upon collision with tilted surfaces, revealing wake-induced circulation as the cause and demonstrating potential applications in biological cleaning.

Contribution

The paper introduces a theoretical model explaining bubble backflipping based on wake-induced circulation, supported by experimental validation and potential practical applications.

Findings

Bubbles with radii 0.6-0.7 mm backflip at surface angles up to 15°

Wake-induced circulation causes the backflipping behavior

Theoretical model aligns well with experimental results

Abstract

Oblique collision of solid particles with surfaces has been a topic of extensive study in Newtonian mechanics, which also explains the motion of bubbles and droplets to some extent. Here, we observe that air bubbles exhibit a backflipping behavior when they collide with a tilted surface. Our experiments reveal that bubbles with radii 0.6-0.7 mm undergo backflipping when they collide with surfaces at an angle of up to 15^o with the strongest backflipping at 3^o. Particle image velocimetry reveals that the backflipping behavior is caused by wake-induced circulation around the bubble, which applies a lift force on the bubble. We develop a theoretical model that incorporates potential flow theory to characterize the circulation caused by the interaction between the bouncing bubble and its wake. The theoretical results are in good agreement with the experiments confirming the key role of the wake-induced lift force in backflipping. Finally, we show that the backflipping behavior of air bubbles can be leveraged for sustainable cleaning of a biological surface coated with a protein solution.