Hydrodynamic stability of rotating, charged and electric-field-exposed drops

J. T. Holgate and M. Coppins

Plasma Physics Group, Imperial College London, London SW7 2BW

Determining the stability of a liquid drop is a fundamental problem in hydrodynamics and aerosol science with industrial applications including fuel injection, microfluidic chips and atomization of drops for mass spectrometry. The breakup of drops also influences natural processes such as the formation and behaviour of thunderstorm clouds. An isolated drop is held together by surface tension but, if a sufficiently strong repulsive force is applied, the drop may split into two or more smaller drops. The breakup processes and stability limits of drops which experience a single repulsive force are well-established: rotating drops deform into an elongated shape with two lobes connected by a thin neck of liquid, which eventually splits into two evenly-sized subdrops, while charged droplets form cone-like tips from which jets of small subdroplets are ejected. The quantitative stability limits for both of these processes have been rigorously confirmed by theory, simulation and experiment. However no such consensus exists for drops which experience multiple repulsive forces; for example experiments show that charged and rotating drops undergo asymmetric fission and hybrid breakup processes involving both necking and cone formation which have not yet been found in the theory. This work explores the breakup of rotating, charged and electric-field-exposed drops through an energy-minimization method applied to spheroidal drops and through numerical simulation.