Influence of shear flow on vesicles near a wall: A numerical study - art. no. 011916

We describe the dynamics of three-dimensional fluid vesicles in steady shea r flow in the vicinity of a wall. This is analyzed numerically at low Reyno lds numbers using a boundary element method. The area-incompressible vesicl e exhibits bending elasticity. Forces due to adhesion or gravity oppose the hydrodynamic lift force driving the vesicle away from a wall. We investiga te three cases. First, a neutrally buoyant vesicle is placed in the vicinit y of a wall that acts only as a geometrical constraint. We find that the li ft velocity is linearly proportional to shear rate and decreases with incre asing distance between the vesicle and the wall. Second. with a vesicle fil led with a denser fluid, we find a stationary hovering state. We present an estimate of the viscous lift force that seems to agree with recent experim ents of Lorz et al. [Europhys. Lett. 51. 468 (2000)]. Third, if the wall ex erts an additional adhesive force, we investigate the dynamical unbinding t ransition that occurs at an adhesion strength linearly proportional to the shear rate.