  Dynamics of non-Brownian flexible fibers in Poiseuille flow between two
parallel planar solid walls is evaluated from the Stokes equations, solved
numerically by an accurate multipole code HYDROMULTIPOLE. Fibers migrate
towards a critical distance from the wall zc, which depends significantly on
the fiber length N and bending stiffness A. Therefore, the calculated values of
zc can be used to sort fibers. Three modes of the dynamics are found, depending
on a shear-to-bending parameter Gamma. In the first mode, stiff fibers deform
only a little and accumulate close to the wall, as the result of a balance
between the tendency to drift away from the channel and the repulsive
hydrodynamic interaction with the wall. This mechanism is confirmed by
simulations in the unbounded Poiseuille flow. In the second mode, flexible
fibers deform significantly and accumulate far from the wall. In both modes,
the tumbling pattern is repeatable. In the third mode, the fibers are even more
curved, and their tumbling is irregular.
