The Effects of Forced Vibration on the Motion of a Large Bubble Under Microgravity

The motion of a large gas bubble in a liquid-filled cell was experimentally and theoretically investigated under microgravity and forced vibration conditions. The experiment was conducted aboard the Space Shuttle during the STS-85 mission using two shallow, cylindrical fluid cells (97.3 mm I.D. × 16.8 mm thickness), each containing a mixture of air/mineral oil (cell #1) and air/water-surfactant solution (cell #2). In microgravity, a large air bubble formed in the middle of the cell, and the cell was oscillated in the direction normal to the cell axis at a specified frequency and amplitude. The bubble responded to periodic cell vibration by translating within at the same frequency but with a different amplitude, and deforming its shape from a circular cross-section to an oval shape. The bubble translation amplitude was found to vary linearly with the cell translation amplitude for both fluid systems. For the low viscosity system (cell #2), the bubble translation amplitude was weakly dependent on the cell vibration frequency and acceleration level. Resonance phenomena were observed at the lowest cell vibration frequencies tested (0.1–0.2 Hz) at which the shape deformation became periodic and the bubble translation amplitude was larger than the values expected from a linear response. A theoretical model was also developed to predict the bubble translation amplitude for both infinite and finite cell sizes, and an inviscid or viscous liquid. The linear two-dimensional model predictions compared well with the measured bubble translation data.