  We use numerical simulations to study the dynamics of three dimensional
vesicles in unconfined and confined Poiseuille flow. Previous numerical studies
have shown that when the fluid viscosity inside and outside the vesicle is same
(no viscosity contrast), a transition from asymmetric slippers to symmetric
parachutes takes place as viscous forcing or capillary number is increased. At
higher viscosity contrast, an outward migration tendency has also been observed
in unconfined flow simulations. In this paper, we study how the presence of
viscosity contrast and confining walls affect the dynamics of vesicles and
present phase diagrams for confined Poiseuille flow with and without viscosity
contrast. To our knowledge, this is the first study that provides a phase
diagram for 3D vesicles with viscosity contrast in confined Poiseuille flow.
The confining walls push the vesicle towards the center while the viscosity
contrast has the opposite effect. This interplay leads to important differences
in the dynamics like bistability at high capillary numbers.
