# Dynamics of front propagation in a compliant channel

## TL;DR

This study experimentally investigates how compliance in a channel affects front propagation, revealing new fingering instabilities and counter-intuitive pushing behavior in air displacing viscous fluid, relevant to pulmonary airway dynamics.

## Contribution

First experimental observation of compliance-induced fingering instabilities and pushing behavior in a model of airway reopening, expanding understanding of interfacial dynamics in compliant channels.

## Key findings

- Compliance induces fingering instabilities absent in rigid channels.
- Counter-intuitive pushing behavior where reduced pressure speeds up flow.
- Transient finger shapes observed over a range of parameters.

## Abstract

Front-propagating systems provide some of the most fundamental physical examples of interfacial instability and pattern formation. However, their nonlinear dynamics are rarely addressed. Here, we present an experimental study of air displacing a viscous fluid within a collapsed, compliant channel - a model system for pulmonary airway reopening. We show that compliance induces fingering instabilities absent in the rigid channel and we present the first experimental observations of the counter-intuitive 'pushing' behaviour previously predicted numerically, for which a reduction in air pressure results in faster flow. We find that pushing modes are unstable and moreover, that the dynamics of the air-fluid front involves a host of transient finger shapes over a significant range of experimental parameters.