VISCOUS FINGERING IN A MAGNETIC FLUID - I - RADIAL HELE-SHAW FLOW

Viscous fingering phenomena in a circular geometry are studied for a m agnetic fluid submitted to a perpendicular magnetic field. Air is inje cted at the center of a Hele-Shaw cell filled with a viscous magnetic fluid. The instability of the interface between the air and the magnet ic fluid is favored by the presence of a magnetic field. More precisel y, the threshold of the instability is magnetic field dependent. The p atterns obtained for high values of the magnetic field with a low inje ction rate are similar to those obtained in the absence of an external field and at high flow rates. We also give a linear analysis for the stability of radial flow under the influence of a magnetic field. This calculation provides us with an understanding of the magnetic field e ffect. (C) 1998 American Institute of Physics.