Ferrofluid hydrodynamics: Waves, jets and free drops

Abstract

A novel approach to hydrodynamical studies uses the bulk force properties of magnetic liquids to probe the dynamics of (i) freely suspended drops; and (ii) unstable surface waves and jets. The fluid dynamics are imaged by a fast CCD camera, allowing thorough analysis of these time-dependent phenomena. Ferrofluid drops are freely suspended in air by using magnetic fields to create an attractive force opposing gravity. The suspended drop then undergoes forced oscillations by perturbing the supporting magnetic field, and exhibits high order nonlinear modes of oscillation which can be driven until the drop bifurcates. Fluid surface waves and jets are investigated in cylindrical geometry. Nonlinear waves are magnetically driven, resulting in dramatic jets when the critical amplitude is exceeded. Such jets are observed to have a maximum acceleration exceeding 700.