COMPUTATIONAL ANALYSIS OF SINGLE RISING BUBBLES INFLUENCED BY SOLUBLE SURFACTANT

The present contribution aims to give an overview of the state-of-the-art in describing fluid interfaces influenced by soluble surfactants, comparing experimental and computational results. Surfactants are amphiphilic molecules subject to ad- and desorption processes at fluid interfaces. In fact, they accumulate at the interface, modifying the respective interfacial properties. Since these interfaces are moving, continuously deforming and expanding, the local time-dependent interfacial coverage and the resulting local effect on surface tension are the most relevant quantities. Direct Numerical Simulation (DNS) provides valuable insights into local quantities such as surfactant distribution and surface tension. The solution procedure is based on the Arbitrary Lagrangian-Eulerian (ALE) Interface-Tracking method for moving meshes, while surfactant transport equations are solved using a collocated Finite Volume and Finite Area Method (FVM/FAM) for transport processes in the bulk and on the interface, respectively. In this work we consider the prototypical case of a single rising bubble in aqueous solutions contaminated by surfactants. A novel approach to simulate such cases with realistic surfactant properties will be presented. The well known issue of thin species boundary layers in advection-dominated transport problems is overcome by the use of a subgrid-scale (SGS) model. The implementation of the SGS model in OpenFOAM in an implicit manner for the surfactant bulk transport and its validation will be presented in this talk. Moreover, the numerical results for rising bubbles in contaminated water obtained applying the SGS model will be shown and compared to the experimental results.