Ferrofluid hydrodynamics: waves, jets and free drops

A novel approach to hydrodynamical studies uses the bulk force properties o f 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 f ast CCD camera, allowing thorough analysis of these time-dependent phenomen a. Ferrofluid drops are freely suspended in air by using magnetic fields to create an attractive force opposing gravity. The suspended drop then under goes forced oscillations by perturbing the supporting magnetic field, and e xhibits high order nonlinear modes of oscillation which can be driven until the drop bifurcates. Fluid surface waves and jets are investigated in cyli ndrical geometry. Nonlinear waves are magnetically driven, resulting in dra matic jets when the critical amplitude is exceeded. Such jets are observed to have a maximum acceleration exceeding 70g.