Flow states and transitions of an active nematic in a three dimensional channel

TL;DR

This study investigates how active nematic fluids transition from turbulence to directed flow in a 3D channel, highlighting the role of flow alignment and channel aspect ratio in flow emergence.

Contribution

It demonstrates the conditions under which net flow occurs in active nematics within 3D channels, linking flow alignment and channel geometry to flow patterns.

Findings

Net flow only occurs with flow-aligning active nematics.

Channel aspect ratio influences the emergence of net flow.

Hydrodynamic screening enables vortex roll formation.

Abstract

We use active nematohydrodynamics to study the flow of an active fluid in a 3D microchannel, finding a transition between active turbulence and regimes where there is a net flow along the channel. We show that the net flow is only possible if the active nematic is flow aligning and that - in agreement with experiments - the appearance of the net flow depends on the aspect ratio of the channel cross-section. We explain our results in terms of the when hydrodynamic screening due to the channel walls allows the emergence of vortex rolls across the channel.