Dynamic fluid-structure interaction of an elastic capsule in the viscous flow

Abstract

The unsteady behavior of a 2D circular elastic capsule is numerically investigated in the three viscous shear flows. The novel idea from the numerical results is verified by an experimental investigation. An Immersed Boundary Method (IBM) has been used to solve the dynamic fluid-structure interaction of the capsule. Computation is carried out in finite parameter ranges where the Reynolds number is Re=0.05~40, and the dimensionless shear rate is G=0.0005~0.05 which is the ratio of the external viscous shear stress to the resistant elastic tensions of the membrane. For the simple shear flow, the inertia effect on the transient behavior of the capsule is studied. For the pulsatile shear flow, two values of the pulsatile period, $T_f$ =1 and $T_f$ =5, are considered for the quasi-steady capsule mechanics. The capsule shows the cyclic structural response that includes subharmonics as the Reynolds number is elevated to Re=10 and 40. The capsule dynamic response includes a phase lag, which is a function of the dimensionless shear rate, as well as the Reynolds number and pulsatile period. The capsule flowing in the Couette flow shows lateral migration due to the transient lift force that is higher for lower G and higher Re. It is found that, when capsules with diverse elasticity are dispersed along the velocity gradient, the capsule with hard membrane has more lift than the one with soft membrane. This numerical results show a application for capsule separation. Experimentally, the difference lateral equilibrium position of a capsule with elasticity is investigated in the Poiseuille flow. Two group of normal hepatocytes (THLE-2) cells with different elasticity are used a model of the elastic capsule. The statistical analysis of the experimental results indicates that the distributions of THLE-2 cells with lower elasticity are shifted to the channel center, relatively higher elasticity. The results are also confirmed and validated by numerical simulations in this s...