Dynamics of an elastic capsule in moderate Reynolds number Poiseuille flow

Abstract

The dynamic motions and lateral equilibrium positions of a two-dimensional elastic capsule in a Poiseuille flow were explored at moderate Reynolds number (10 c Re. 100) as a function of the initial lateral position (y(0)), Re, aspect ratio (epsilon), size ratio (lambda), membrane stretching coefficient (phi) and bending coefficient (gamma). The transition between tank-treading (TT) and swinging (SW) to tumbling (TU) motions was observed and the lateral equilibrium positions of the capsules varied according to the conditions. The initial behavior of the elastic capsule was influenced by variation in the initial lateral position (y(0)), but the equilibrium position and dynamic motion of the capsule were not affected by such variation. The capsules had a stronger tendency toward TU motion at higher values of Re, phi and gamma, whereas the capsules underwent TT or SW motion as the values of epsilon and lambda increased. Under moderate Re Poiseuille flows, capsules tended to migrate across streamlines to a specific equilibrium position. The lateral equilibrium position shifted toward the centerline at larger lambda and migrated toward the wall at larger epsilon, phi and gamma. As Re increased, the equilibrium position first shifted toward the bottom wall, then toward the channel center. However, different equilibrium position trends were obtained around the SW-TU transition. The capsule undergoing TU motion tended to migrate downward toward the bottom wall more than the capsule undergoing SW motion, all other conditions being similar. (C) 2012 Elsevier Inc. All rights reserved.