Numerical Simulation Of Air Bubbles Rising In Water Using An AxisynmetricVOF Method

Abstract

Multiphase flows occur in numerous technological and environmental applications. However, the diversity of flow types makes a general description of such flows impossible, necessitating fundamental research in this area. Understanding the motion of gas bubbles in a liquid is a problem of both scientific and engineering importance. The rise of a single bubble of air through water, for which experimental data have been published, is also a good test problem for CFD code validation. In this paper, a volume of fluid (VOF) method is used to simulate fuid flow and track the interface. We present a piecewise linear interface calculation (PLIC) method in axisymmetric geometries, which is somewhat more complex than the corresponding procedure for reconstructing a planar interface on Cartesian grids that has been described in two and three dimensions in other papers. We incorporate this VOF method into the RIPPLE code, a 2D Eulerian code written for free surface flows, which implements the continuum surface force (CSF) model to account for surface tension effects. We validate the code by comparing the evolution of the shape of a bubble and its terminal velocity with experimental data for different size bubbles. We also compare results obtained with PLIC to those using the simple line interface calculation (SLIC) for a 3 mm bubble, demonstrating improved accuracy for the PLIC scheme.