Trigger turbulent bands directly at low Reynolds numbers in channel flow using a moving-force technique

TL;DR

This paper introduces a novel moving-force technique in direct numerical simulations that can trigger and control turbulent band patterns at low Reynolds numbers in channel flow, down to Re ≈ 500.

Contribution

The authors develop a method to directly generate and manipulate turbulent bands at low Reynolds numbers, enabling detailed study of band interactions and transition mechanisms.

Findings

Turbulent bands can be triggered at Re ≈ 500.

The method allows precise control over band position and orientation.

It outperforms traditional perturbation approaches in low-Re regimes.

Abstract

We show a method, for direct numerical simulations, to trigger and maintain turbulent bands directly at low Reynolds numbers in channel flow. The key is to impose a moving localised force which induces a local flow with sufficiently strong inflectional instability. With the method, we can trigger and maintain turbulent bands at Reynolds numbers down to $Re \simeq 500$. More importantly, we can generate any band patterns with desired relative position and orientation. The usual perturbation approach resorts to turbulent fields simulated at higher Reynolds numbers, random noise, or localised vortical perturbation, which neither assures a successful generation of bands at low Reynolds numbers nor offers a control on the orientation of the generated bands. A precise control on the position and orientation of turbulent bands is important for the investigation of all possible types of band interaction and for understanding the transition in channel flow at low Reynolds numbers.