Direct Numerical Computation of the Lift Force on Single Bubbles

In addition to experimental investigations, computational fluid dynamics is frequently applied to obtain a better understanding of multiphase flows in industrial devices. An accurate simulation of the bubbles’ movement requires detailed knowledge of the interacting forces between gas and liquid phase. In typical gas-liquid flows, bubbles rise in non-homogenous velocity fields. In this case, the bubbles experience a so-called lift force which causes them to migrate sideward, while they are rising. In air-water systems, small spherical bubbles usually drift into the direction of higher counter-flow, whereas larger, more deformed bubbles drift in the opposite direction. In this contribution, we present numerical simulations of single bubbles rising in linear shear flows. The influence of bubble size and shape on the lift force is shown and the results are compared with experimental investigations carried out by Tomiyama and co-workers [1]. The simulations are performed with the MPI-parallelized code FS3D (Free Surface 3D) which employs an advanced Volume-of-Fluid method to resolve free and deformable gas-liquid interfaces [2]. FS3D was developed at the ITLR, University of Stuttgart and extended in our group for the current studies. Bubble size and material data are varied, and the corresponding lift forces in a linear shear flow are calculated by evaluation of the bubble trajectories.