Bubbles Motion under Water: with and without Shear Stress

Description: Bubble dynamics sit at the heart of chemical engineering, since the rise, deformation, and coalescence of bubbles govern the gas-liquid interfacial area — and therefore mass transfer and reaction rates — in equipment such as bubble columns, aeration tanks, and gas-liquid contactors. This project simulates bubble motion rising through water over a plate, comparing cases with and without surface tension to assess how significantly this interfacial force affects bubble shape and behavior when the free surface between phases matters.

Methodology: The 2D geometry, built in SpaceClaim, spans 50 mm long by 65 mm high and is meshed in ANSYS Meshing with a structured grid of 81,250 elements. The Volume of Fluid model tracks the two Eulerian phases — air and water — using a sharp interfacial interface with explicit formulation, alongside a laminar viscous model, an initial bubble size of 2 × 10⁻⁴ m, and gravity applied at −9.81 m/s² along the Y-axis; the case is solved as transient using a pressure-based solver, SIMPLE pressure-velocity coupling, PRESTO! for pressure, second-order upwind for momentum, and a compressive scheme for volume fraction, with the domain initialized as fully patched with water and run over 1,900 adaptive time steps of 0.0002 s each. Two otherwise identical cases are compared, differing only in whether surface tension is included.

Analysis: The results show, through the resulting bubble shapes, how significantly the simulation is affected when surface tension is omitted: without it, the bubble fails to hold its form and collapses under the surrounding water pressure, rather than maintaining the coherent shape that surface tension would otherwise sustain. This underlines the importance of including interfacial forces when modeling bubble behavior, a key consideration for accurately predicting interfacial area and mass transfer in chemical-process equipment.