Hydrodynamic Forces Acting on Vertically Rising Bubbles

The forces acting on vertically rising bubbles are investigated. By constructing force balances, the terminal rise velocity and rise velocity over time of spherical and deformable bubbles are determined and compared to literature and simulations carried out by Basilisk. Good agreement is found between the derived expressions and literature. The simulations show slightly less applicability for determining the rise velocity for small bubble diameters and lack accuracy for larger bubble sizes. In a side-by-side rising configuration, the bubbles may attract or repel each other, depending on the rise Reynolds number (Re). The mechanisms leading to this behaviour are covered extensively. Additionally, low Re side-by-side rise (Re < 1) causes bubble pairs to rise faster than their single counterpart. Simulations are carried out to obtain insight into this phenomenon. It is discovered that the fluid velocity between the bubbles rising at low Re is larger than that for bubbles rising at increased Re. The role of the fluid velocity in the gap between the bubbles and the pressure distribution around the bubbles in the low Re-regime are interesting topics for future research.