Unsteady Dynamics of Vesicles in a Confined Poiseuille Flow

The dynamic behaviors of a single vesicle bounded by the cylindrical wall in a Poiseuille flow were investigated by considering different confinements and dimensionless shear rates. By observing the evolution of two adjacent particles attached to the internal and external surfaces of the spherical vesicles, we found they had the same frequency. The vorticity trajectories formed by the time-tracing of the particles on the membrane are parallel, which can be identified as the unsteady rolling motion of the membranes due to the unfixed axis. The dynamic behaviors of vesicles are associated with the confinement degree and the dimensionless shear rate. The smaller dimensionless shear rate will result in the slower frequency of the rolling by examining the velocity of the rolling. The weakened rolling motion under stronger confinements is observed by measuring the evolution of the orientation angles. The changes of revolution axes over time can be interpreted by the lateral excursion of the center of mass on the orthogonal plane of the flow.