  We present a numerical analysis of the lateral movement and equilibrium
radial positions of red blood cells (RBCs) with major diameter of 8 $\mu$m
under a Newtonian fluid in a circular channel with 50-$\mu$m diameter. Each
RBC, modelled as a biconcave capsule whose membrane satisfies strain-hardening
characteristics, is simulated for different Reynolds numbers $Re$ and capillary
numbers $Ca$, the latter of which indicate the ratio of the fluid viscous force
to the membrane elastic force. The effects of initial orientation angles and
positions on the equilibrium radial position of an RBC centroid are also
investigated. The numerical results show that depending on their initial
orientations, RBCs have bistable flow modes, so-called rolling and tumbling
motions. Most RBCs have a rolling motion. These stable modes are accompanied by
different equilibrium radial positions, where tumbling RBCs are further away
from the channel axis than rolling ones. The inertial migration of RBCs is
achieved by alternating orientation angles, which are primarily affected by the
initial orientation angles. Then the RBCs assume the aforementioned bistable
modes during the migration, followed by further migration to the equilibrium
radial position at much longer time periods. The power (or energy dissipation)
associated with membrane deformations is introduced to quantify the state of
membrane loads. The energy expenditures rely on stable flow modes, the
equilibrium radial position of RBC centroids, and the viscosity ratio between
the internal and external fluids.
