LES of turbulent bubble formation and break-up based on interface tracking

A 3D finite-difference method featuring piecewise planar volume tracking and explicit sub-arid scale modeling is used to simulate the violent, turbulent bubbling resulting from air venting into a water pool through a downcomer pipe. A moderate-sized mesh and domain decomposition-based parallelism were used for a O(10(5))-O(10(6))-timestep computation, in order to extract turbulence statistics representative of long-time simulation of fully-developed flow. Volume tracking is seen to be a robust basis for super-grid scale simulation of the bubble rise, fragmentation and coalescence phenomena; it captures the kinematics of interfaces that are adequately resolved on the grid, and preserves the existence of bubbles and liquid jets breaking up to grid-scale (1-2 cells) size. Interface deformations are seen to strongly correlate with the large-scale structures forming at the front in the gas phase. Enhanced energy decay according to the 8/3 power law seen in bubbly flow is generally attained, with also some tendency towards the Kolmogorov K41 slope. The bubbling is turbulent on the gas side, and the main sources of turbulence are bubble break-up and gas jetting from the downcomer tip.