Abstract

We describe the dynamics of three-dimensional fluid vesicles in steady shear flow in the vicinity of a wall. This is analyzed numerically at low Reynolds numbers using a boundary element method. The area-incompressible vesicle exhibits bending elasticity. Forces due to adhesion or gravity oppose the hydrodynamic lift force driving the vesicle away from a wall. We investigate three cases. First, a neutrally buoyant vesicle is placed in the vicinity of a wall that acts only as a geometrical constraint. We find that the lift velocity is linearly proportional to shear rate and decreases with increasing distance between the vesicle and the wall. Second. with a vesicle filled 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 experiments of Lorz et al. Europhys. Lett. 51. 468 (2000). Third, if the wall exerts an additional adhesive force, we investigate the dynamical unbinding transition that occurs at an adhesion strength linearly proportional to the shear rate.

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