DNS of the wall effect on the motion of bubble swarms

This paper presents a numerical study of the gravity-driven motion of single bubbles and bubble swarms through a vertical channel, using High-Performance Computing (HPC) and Direct Numerical Simulation (DNS) of the Navier-Stokes equations. A systematic study of the wall effect on the motion of single deformable bubbles is carried out for confinement ratios CR = {2, 4, 6} in both circular and square channels, for a broad range of flow conditions. Then, the rising motion of a swarm of deformable bubbles in a vertical channel is researched, for void fractions alpha = {8.3%, 10.4%, 12.5%} and CR = {4, 6}. These simulations are carried out in the framework of a novel multiple marker interface capturing approach, where a conservative level set function is used to represent each bubble. This method avoids the numerical and potentially unphysical coalescence of the bubbles, allowing for the collision of the fluid particles as well as long time simulations of bubbly flows. Present simulations are performed in a periodic vertical domain discretized by 2 x 10(6) control volumes (CVs) up to 16.6 x 10(6) CVs, distributed in 128 up to 2048 processors. The collective and individual behavior of the bubbles are analyzed in detail. (C) 2017 The Authors. Published by Elsevier B.V.