Numerical Analysis of a Single Bubble by VOF Method.

In order to examine the feasibility of direct simulation of bubbly flow, the applicability of the VOF (volume of fluid) method to analyses of a single rising bubble was examined in this study. Calculated bubble shapes and terminal velocities under wide ranges of Eotvos number and Morton number were compared with the experimental data summarized by Grace et al. Except for the cases in which bubble shapes were spherical-cap and skirted, the VOF method could predict them well by assigning only eight cells to the bubble diameter. Hence, it was confirmed that some modification of this method will enable us to simulate bubbly flow directly under a wide range of flow conditions. The relationship between bubble shape and velocity distribution was also examined within the ranges in which the VOF method is valid. It was found that the secondary vortex appearing in wobbling bubbles induces a velocity component normal to the bubble interface, and this velocity is one of the causes of the wobbling shape of the bubble.