Rising Bubble in a Vertical Slowly Diverging Pipe

Abstract

We present the results of a combined experimental and numerical study of an air bubble rising in a vertical slowly diverging pipe in a stagnant liquid. Initially, the bubble is confined in a cylindrical tube and rises due to buoyancy in the same manner as a Taylor or elongated bubble. When the bubble moves upwards, it reduces its vertical height and the shape of the bubble transitions to a spherical cap bubble. Different tests with various liquids are reported and a numer- ical simulation using two-dimensional axisymmetric finite element method for two-phase flow is reported. An adaptative mesh is also used to compute the bubble dynamics. The experimental and the simulation results are compared in terms of rising velocity and bubble aspect ratio. Our results show a puzzling feature that is the bubble dynamics and topology strongly depends on the initial conditions.