The role of diffusion and transient velocities in the dispersal of
passive scalars by chaotic advection produced in a low Reynolds
number periodic journal-bearing flow is studied numerically and
experimentally. The transient velocity field, which occurs whenever
the cylinders switch motion, is obtained by solving the
Navier–Stokes equations numerically in the eccentric annulus. It is
observed, numerically, that the transient effects, along with
diffusion, significantly enhance the separation of chaotically
advected particles even when the Reynolds number is very low.
Corresponding experimental observations are found to be in good
qualitative agreement with the numerical results obtained by
including the effect of transient velocities, which are seen to add
to the overall separation of particles.