Electronic edition ISSN 1574-0579

Stability of two flowing coaxial ferrofluid annuli

S. H. Ferguson Briggs¹ , M. G. Blyth² , A. J. Mestel¹

¹ Mathematics Department, Imperial College London SW7 2BZ, UK
² University of East Anglia, Norwich, NR4 7TJ, UK

Abstract
Two concentric ferrofluid annuli fill the gap between two concentric cylinders. In a stationary state without magnetic field, the interface between the fluids is unstable to surface tension. However, this instability can be controlled either by axial motion if the fluids have different viscosity, or by passing a current down the inner cylinder if the inner fluid has a higher magnetic susceptibility. If the susceptibilities differ, an axial magnetic field may also grant stability to all but the longest wavelengths. Each of these mechanisms can, however, give rise to other instabilities. This paper investigates the linear stability to arbitrary disturbances of the combination of shear and magnetic effects. Figs 5, Refs 14.