Bubbles in viscous liquids: shapes, wakes and velocities

TLDR

The authors visualized the flow around rising bubbles using hydrogen bubble tracers and a synchronized cine camera to capture streamlines. The study quantified bubble shapes and terminal velocities in viscous liquids, showing that for Morton numbers above 4 × 10⁻³ the drag coefficient and shape depend solely on Reynolds number, with closed laminar toroidal wakes at R < 110 and open unsteady wakes at R > 110, and correlating shape regimes and rise velocities across 7.4 × 10⁻⁴ < M < 850 and R < 150.

Abstract

The shapes and terminal velocities of bubbles rising in viscous liquids have been determined. For Morton numbers (M) greater than 4 × 10−3 the drag coefficient and dimensionless bubble shape are functions only of Reynolds number (R). Shape regimes and terminal rise velocities have been correlated. The flow field around a rising bubble was visualized through the hydrogen bubble tracer technique. For M > 4 × 10−3 and R < 110 the bubbles trailed closed, laminar toroidal wakes. For R > 110 the wake was open and unsteady. Streamlines for the flow were obtained by raising a ciné camera at the same speed as the bubble and filming the H2 tracer bubbles. Results are presented for R < 150 and 7·4 × 10−4 < M < 850.