Vortex generation by an oscillatory magnetic obstacle

A. Beltrán, - S. Cuevas - E. Ramos

Centro de Investigación en Energ\'ia, Universidad Nacional Autónoma de México A.P. 34, Temixco, Mor. 62580, MEXICO

Abstract
The flow patterns generated when a localized magnetic field (a magnetic obstacle) oscillates in a quiescent conducting fluid layer are explored in two cases: a) in the absence of injected electric currents, and b) with an injected DC current in a direction parallel to the axis of oscillation of the magnetic field. In case a), numerical simulations reveal complex flow structures, where vortex pairs are created periodically and expelled from the neighbourhood of the magnetic obstacle as new vortices appear. The dynamics is described and interpreted in terms of the points, where the velocity vanishes (critical points). Case b) was analyzed experimentally in a thin electrolytic layer with a permanent magnet oscillating with frequencies in the range 0.3 -- 2 Hz. For a restricted frequency range, in the neighbourhood of the magnetic obstacle, local vortical structures are formed and shed periodically along the main direction of the applied Lorentz force. Numerical simulations are compared with experimental observations. This flow shows that harmonic oscillations of a localized magnetic field may lead to unstable flow behaviour. Figs 4, Refs 10.