Deformation of a single red blood cell in bounded Poiseuille flows

An immersed boundary method (IBM) combined with the elastic spring model is applied to investigate the deformation of a single red blood cell (RBC) in two-dimensional bounded Poiseuille flows. The equilibrium shape of the cell under flow depends on the swelling ratio (($s^*$)), the initial angle of the long axis of the cell at the centerline ($\varphi$), the maximum velocity of the flow ($u_\textrm{max}$), the membrane bending stiffness of the RBC ($k_b$), and the height of the microchannel($H$). Two motions of oscillation and vacillating breathing of the RBC are observed in narrow channel considered here. The strength of the vacillating-breathing motion depends on degree of confinement and $u_\textrm{max}$. For the different $k_b$, the RBC obtains the same equilibrium shape for the same capillary number. Parachute shape and bullet-like shape, depending on the angle $\varphi$, coexist for the elliptic shape cell with lower $u_\textrm{max}$ in a narrower channel.