# Oblate to prolate transition of a vesicle in shear flow

## TL;DR

This study uses numerical simulations to explore how vesicles transition from oblate to prolate shapes in shear flow, revealing coexistence regions, transition boundaries, and lift dynamics near critical flow conditions.

## Contribution

It provides detailed analysis of shape coexistence, transition boundaries, and transition times for vesicles in shear flow, including confined conditions and weak flow regimes.

## Key findings

- Coexistence of oblate and prolate shapes depends on flow parameters.
- Transition time diverges near the critical Capillary number.
- Lift dynamics of vesicles are characterized in weak flow regimes.

## Abstract

Vesicles are micrometric soft particles whose the membrane is a two-dimensional incompressible fluid governed by bending resistance leading to a zoology of shapes. The dynamics of deflated vesicles in shear flow with a bottom wall, a first minimal configuration to consider confined vesicles is investigated using numerical simulations. Coexistence under flow of oblate (metastable) and prolate (stable) shapes is studied in details. In particular, we discuss the boundaries of the region of coexistence in the (v, Ca) plane where v is the reduced volume of the vesicle and Ca the Capillary number. We characterize the transition from oblate to prolate and analyse the divergence of the transition time near the critical capillary number. We then analyse lift dynamics of oblate vesicle in the weak flow regime.