[Seminar] Instability and turbulence in electroconvective flows

Speaker

Dr. Feng Zhe - National University of Singapore 

Title

Instability and turbulence in electroconvective flows

Abstract

The electroconvective (EC) flow refers to the convective motion induced by an electrical potential difference applied to two planar electrodes covered by ion-exchange membranes (IEM). It has been widely applied in many industrial procedures, such as the electrohydrodynamic (EHD) pumping and EHD mixers. Nevertheless, a long-standing discrepancy of linear instability criteria (i.e. potential difference) between the experiment and theory exists in this flow. This work hypothesizes that imperfections on IEMs in the experiment may result in a mismatch between the theoretical modelling and experimental conditions. By considering these perturbations in our numerical simulations and global stability analyses, we found that the linear instability criteria are reduced and closer to experimental values. Chaotic characteristics of the EC flow have also been studied using Lyapunov exponents, revealing the high dimensionality and extensive nature of EC chaos. In turbulent EC flows, a flow topology transition is observed after which the electric transfer efficiency abruptly decreases. Additionally, when above EC motion is subjected to a through-flow, its linear and nonlinear spatiotemporal instability criteria are found to be consistent with each other, and those nonlinear finite-amplitude solutions in its subcritical range are indicated to be convectively unstable.

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