Effect of Low–Frequency Vibrations on the Hydrodynamic Properties of Single Bubbles at Different Gravity Levels

A key aspect of space application technology is the generation and control of multi–phase flows. The efficiency of mass and heat transfer can be significantly improved by adding bubbles or droplets into continuous phases. The effects of the ratio of amplitude to bubble diameter (A/D), Bond number (Bo), and different gravity levels (G/g) on bubble centroid motion and shape oscillation are fully analyzed using the VOF method to understand the bubble–centroid trajectory and shape–oscillation mechanism under low–frequency vibrations. The present studies show that A/D, Bo, and G/g have important effects on bubble trajectory and shape oscillation. There are two types of oscillations for bubble shape: regular oscillation and chaotic oscillation. As Bo and A/D increase, bubble oscillation in a gravity–free environment changes from regular to chaotic oscillation. For the present results, bubble oscillations at different gravity levels (except zero–gravity level) are chaotic oscillations. Three types are recognized for the bubble–centroid motion: levitation, rising and sinking. When both A/D and Bo are tiny, a bubble is hung in its initial position in a gravity–free environment. Bubble–centroid motion changes from sinking to rising with an increase in A/D and Bo. The higher the gravity level is, the shorter the time taken for the bubble to rise is. The change in the flow field seems to be mainly caused by the vibration of fluid particles, almost independent of the level of gravity. The flow field becomes more chaotic as A/D and Bo increase.