Mixing-induced global modes in open active flow

TL;DR

This paper analyzes how local mixing in open active flows can induce a transition from convective to absolute instability, leading to global modes, with analytical and numerical validation.

Contribution

It introduces an analytical framework for predicting the transition to global modes caused by mixing in open active flows, supported by numerical simulations.

Findings

Mixing can induce absolute instability in convectively unstable flows.

The transition point is analytically derived based on effective diffusion.

Numerical simulations confirm the theoretical predictions.

Abstract

We describe how a convectively unstable active field in an open flow configuration becomes absolutely unstable due to local mixing. A representation of the mixing region as those with locally enhanced effective diffusion allows us to find the linear transition point to unstable global mode analytically. We derive the critical exponent characterizing weakly nonlinear regimes beyond instability and compare it with numerical simulations of a full two-dimensional flow problem.