Path Instabilities of Bubble Rising in Polymer Solutions of Hele–Shaw Cell

概要

論文の詳細を見る
The buoyancy-driven path instabilities of an air bubble rising in a Hele–Shaw cell filled with pure water and aqueous poly(N-isopropyl acrylamide) (PNIPAM) solutions are examined as a function of the Eötvös number ($\mathit{Eo}$) by measuring changes in the bubble shape, the trajectory, and the peripheral length of a bubble ($L$) as well as the visualization of the wake structures behind the bubble. The instabilities can be categorized into four regimes: (1) an oblate ellipse bubble accompanied with a vibrational trajectory, no changes in $L$, and a Kármán vortex street for the wake structure, (2) a comma-shaped bubble with a vibrational motion of both path and $L$, together with a vortex street different from a Kármán one, and (3) changes in the bubble shape, such as a comma-shaped bubble and a jellyfish one with a vibration of both path and $L$ accompanied with a vortex street different from a Kármán one, and (4) changes in the bubble shape, such as a bird flapping its wings bubble and a jellyfish one with a straight trajectory, a vibration of $L$, and no vortex streets. However, in the PNIPAM solution, vibrations of path and $L$ are somewhat suppressed by adsorption of PNIPAM on the bubble surface and no bird flapping its wings bubble is observed.
2009-11-15