Path Instabilities of Rising Air Bubbles in a Hele-Shaw Cell

Abstract

The path of a circular air bubble rising in a viscous fluid of a Hele-Shaw cell is found to change from a straight path to a zigzag path when the Reynolds number of the bubble (proportional to the bubble terminal velocity) exceeds a threshold. By visualizing the wake structures of the rising bubbles, and measuring the actual paths of the bubbles, we demonstrate that the path instability is a consequence of the vortex shedding behind the bubble.