Vesicles in a Poiseuille flow

TL;DR

This paper presents a small-deformation analytical model for vesicle dynamics in Poiseuille flow, revealing migration behaviors, shape coexistence, and the effects of viscosity ratios, providing new physical insights into vesicle motion.

Contribution

It introduces a quantitative analytical framework for vesicle behavior in flow, highlighting migration patterns, shape coexistence, and the influence of viscosity ratios, which advances understanding beyond previous models.

Findings

Vesicles migrate towards the flow centerline at low viscosity ratios.

Above a critical viscosity ratio, vesicles tumble and cross-stream migration stops.

Two distinct vesicle shapes coexist at the flow centerline under certain conditions.

Abstract

Vesicle dynamics in unbounded Poiseuille flow is analyzed using a small-deformation theory. Our analytical results quantitatively describe vesicle migration and provide new physical insights. At low ratio between the inner and outer viscosity $\lambda$ (i.e. in the tank-treading regime), the vesicle always migrates towards the flow centerline, unlike other soft particles such as drops. Above a critical $\lambda$, vesicle tumbles and cross-stream migration vanishes. A novel feature is predicted, namely the coexistence of two types of nonequilibrium configurations at the centreline, a bullet-like and a parachute-like shapes.