Numerical study on the shear-induced lift force acting on a spherical bubble in aqueous surfactant solutions

A single bubble motion in aqueous surfactant solutions is discussed in this paper. We focus on the change of the lift force acting on a bubble in a linear shear flow under the condition that the bubble surface is contaminated by surfactant adsorption which leads the Marangoni effect. With an increase of Langmuir number which corresponds to a decrease of desorption rate constant of surfactant, the lift force acting on a spherical bubble decreases from the value of a clean bubble to near zero. This reduction is significantly related to a nonaxisymmetric distribution of pressure on the surface. Comparing the present results with those of our previous simulations using an axisymmetric stagnant cap model, the lift coefficients in the present simulations show larger values than those of the stagnant cap model. This is due to a nonaxisymmetric distribution of surface concentration. This asymmetry of the distribution enhances the asymmetry of the surface pressure distribution, which ends up the larger shear-induced lift force than that of the axisymmetric stagnant cap model.