Vesicle dynamics in confined steady and harmonically modulated Poiseuille flows

TL;DR

This study numerically investigates the complex oscillatory behaviors of vesicles in confined Poiseuille flows, including steady and modulated flows, revealing coexistence of shapes and dynamic transitions influenced by flow parameters.

Contribution

It introduces a detailed numerical analysis of vesicle dynamics under flow modulation, highlighting new oscillatory states and shape coexistence phenomena.

Findings

Identification of centered snaking oscillations in vesicles

Coexistence of multiple vesicle shapes in parameter space

Flow modulation induces shape transitions and oscillation modulation

Abstract

We present a numerical study of the time-dependent motion of a two-dimensional vesicle in a channel under an imposed flow. In a Poiseuille flow the shape of the vesicle depends on the flow strength, the mechanical properties of the membrane, and the width of the channel as reported in the past. This study is focused on the centered snaking (CSn) shape, where the vesicle shows an oscillatory motion like a swimmer flagella even though the flow is stationary. We quantify this behavior by the amplitude and frequency of the oscillations of the vesicle's center of mass. We observe regions in parameter space, where the CSn coexists with the parachute or the unconfined slipper. The influence of an amplitude modulation of the imposed flow on the dynamics and shape of the snaking vesicle is also investigated. For large modulation amplitudes transitions to static shapes are observed. A smaller modulation amplitude induces a modulation in amplitude and frequency of the center of mass of the snaking vesicle. In a certain parameter range we find that the center of mass oscillates with a constant envelope indicating the presence of at least two stable states.