Dynamic modes of a capsule under oscillating shear flow with finite inertia

Abstract

Inertia may significantly influence the transient deformation process and the steady-state structure of a deformable capsule. The behavior of a two-dimensional deformable capsule in shear flow at finite Reynolds numbers (Re) is studied numerically. By simulating numerous cases with different Re and frequencies (f), we observed persistent oscillation, asymmetric oscillation, deflected oscillation, and stable modes. The phase diagram in the Re-f plane is presented. At low frequencies, a capsule shows a phase-lag phenomenon between the deformation and the applied shear. At moderate frequencies, the anomaly of decreasing maximum deformation with increasing Re is observed. The anomaly is attributed to the mode shift. In addition, a scaling law of the maximum deformation of the capsule as a function of Re and f is proposed. The study may shed some light on the identification and screening of cells in vitro, as well as the transport and breakup of cells in vivo.