Numerical Simulation of Bubbles in Shear Flow

Abstract

AbstractTo gain a basic understanding of foam flow, as it can be found e.g. in transport of aerated food, simulation tools can help to provide better insight. Shearing of the bubbles appears in different flow geometries and is for a bubble assembly not captured analytically. Also experimentally, those flow fields are hard to observe so that simulations are the method of choice.Our method to simulate foams uses a volume of fluid approach that is based on the free surface algorithm by Körner et al. [1]. Different from classical multiphase methods, only the liquid phase is simulated and special boundary conditions at the liquid‐gas interface account for the gas phase. With this approach high density ratios, e.g. in water‐air systems, are easier to realize than in other methods. High density ratios are even necessary to physically justify the model, where the dynamics of the lighter phase are partially neglected. This method is integrated in the Lattice Boltzmann software framework waLBerla [3] (widely applicable Lattice Boltzmann solver from Erlangen†) that can be used on massively parallel computers and thus allows to simulate even large bubble assemblies.As first validation, single bubbles are sheared with different capillary numbers and the simulation results are compared to literature [2] and show good agreement. The next step is shearing a bubble assembly which is arranged like a dense sphere packing. In order to investigate the geometrical configuration of the assembly and its impact on the behavior during a shear deformation, the bubble assembly is rotated with different angles with respect to the shear direction. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)