  Computational modeling and simulation are presented on the motion of red
blood cells behind a moving interface in a capillary. The methodology is based
on an immersed boundary method and the skeleton structure of the red blood cell
(RBC) membrane is modeled as a spring network. The computational domain is
moving with either a designated RBC or an interface in an infinitely long
two-dimensional channel with an undisturbed flow field in front of the domain.
The tanking-treading and the inclination angle of a cell in a simple shear flow
are briefly discussed for the validation purpose. We then present the results
of the motion of red blood cells behind a moving interface in a capillary,
which show that the RBCs with higher velocity than the interface speed form a
concentrated slug behind the interface.
