Dual ferrohydrodynamic and electrohydrodynamic flow instabilities and patterns in uniform dc, ac and rotating fields

Continuum electromechanics of ferrohydrodynamic interactions in magnetic liquids (ferrofluids) and dual electrohydrodynamic interactions with polarizable dielectric liquids are described and compared. Simple dual experiments presented include: the rise of ferrofluid around a current-carrying wire and the rise of dielectric liquid between diverging electrodes; ferrohydrodynamic and electrohydrodynamic peaking interfacial instability with a perpendicular magnetic or electric field; and electric and magnetic labyrinth instability when a thin layer of magnetic or dielectric fluid is stressed by a uniform magnetic or electric field parallel to the thin dimension of the interface. New spiral and droplet patterns that form in combined DC and rotating uniform magnetic fields are presented for magnetic liquids.