Transition routes of electrokinetic flow in a divergent microchannel with bending walls

TL;DR

This study experimentally investigates how AC electrokinetic flow transitions to chaos and turbulence in a divergent microchannel with bending walls, revealing frequency-dependent response behaviors and bifurcation mechanisms.

Contribution

It provides new experimental insights into the transition routes and bifurcation phenomena of electrokinetic flow under AC electric fields in microchannels.

Findings

Flow responds at both neutral and AC frequencies when f_f<30 Hz.

Flow responds only at neutral frequency when f_f>=30 Hz.

Periodic doubling and subcritical bifurcations observed during transition.

Abstract

Electrokinetic flow can be generated as a highly coupled phenomenon among velocity field, electric conductivity field and electric field. It can exhibit different responses to AC electric fields in different frequency regimes, according to different instability/receptivity mechanisms. In this investigation, by both flow visualization and single-point laser-induced fluorescence (LIF) method, the response of AC electrokinetic flow and the transition routes towards chaos and turbulence have been experimentally investigated. It is found, when the AC frequency $f_f<30$ Hz, the interface responds at both the neutral frequency of the basic flow and the AC frequency. However, when $f_f>=30$ Hz, the interface responds only at the neutral frequency of the basic flow. Both periodic doubling and subcritical bifurcations have been observed in the transition of AC electrokinetic flow. We hope the current investigation can promote our current understanding on the ultrafast transition process of electrokinetic flow from laminar state to turbulence.