Field-induced Hydrodynamic Instability

Hydrodynamic flows are sometimes stable, but often unstable. This lies in an inherent stability to sustain flows against small perturbations14. Such stability problem expands to electrically conducting fluids in the presence of electric fields. This electrohydrodynamic (EHD) stability associates with various engineering applications such as electrospray ionization and electrostatic spinning. Coupling the basic concepts in continuum electromechanics and hydrodynamic stability, the pioneering works by Melcher, Taylor, and Levich, successfully described EHD instability in those systems. Recently, a new example of EHD stability was uncovered on ion exchange membranes, i.e. electroconvection (EC). Selective ion flux through the membranes drives the strong depletion of co- ions, generating unstable charge separation layers and vortical flows. This phenomenon also has a significant relevance in practical applications including electro-membrane/-chemical systems.

Our model platform of the field-induced hydrodynamic instability (i.e. EC) enjoys a great controllability by decoupling the source of instability and fluid flows4, 7. By using this platform, we aim to elucidate i) EC’s vortex structures (e.g. vortex asymmetry and 3D patterns) and ii) the dynamics of chaotic EC compared with conventional inertia-driven instability & turbulence. Also, we will explore complex situations in practical systems, where EC occurs with iii) other sources of hydrodynamics instabilities (e.g. temperature / chemical gradients), and/or in iv) other fluid environments (e.g. porous media flow, non-Newtonian fluids, field-activated fluids).