Modeling bubbles and droplets in magnetic fluids

Abstract

We develop, test and apply a volume of fluid (VOF) type code for the direct numericalsimulation of two-fluid configurations of magnetic fluids with dynamic interfaces.Equilibrium magnetization and linear magnetic material are assumed and uniform imposedmagnetic fields are considered, although extensions to nonlinear materials andto fields with spatio-temporal variability are possible. Models are computed forconfigurations of bubbles of non-magnetic fluid rising in ferrofluid and dropletsof ferrofluid falling through non-magnetic fluid. Bubbles and droplets exhibitsimilar changes of shape in the presence of vertical fields, due to a combinationof elongation along the field lines and the fluid dynamics of ordinary rising orfalling at small Bond number. Bubbles become more prolate than droplets underthe same parameters and are accordingly found to break up more readily thandroplets in stronger fields. Indirect effects are observed, such as the change in risetime and the consequent changes in the flow due to increased Reynolds number.