Structure of the Wake of a Magnetic Obstacle

We use a combination of numerical simulations and experiments to elucidate the structure of the flow of an electrically conducting fluid past a localized magnetic field, called magnetic obstacle. We demonstrate that the stationary flow pattern is considerably more complex than in the wake behind an ordinary body. The steady flow is shown to undergo two bifurcations (rather than one) and to involve up to six (rather than just two) vortices. We find that the first bifurcation leads to the formation of a pair of vortices within the region of magnetic field that we call inner magnetic vortices, whereas a second bifurcation gives rise to a pair of attached vortices that are linked to the inner vortices by connecting vortices.Comment: 4 pages, 5 figures, corrected two typos, accepted for PR

Flow and magnetic structures in a kinematic ABC-dynamo

Dynamo theory describes the magnetic field induced by the rotating, convecting and electrically conducting fluid in a celestial body. The classical ABC-flow model represents fast dynamo action, required to sustain such a magnetic field. In this letter, Lagrangian coherent structures (LCSs) in the ABC-flow are detected through Finite-time Lyapunov exponents (FTLE). The flow skeleton is identified by extracting intersections between repelling and attracting LCSs. For the case A = B = C = 1, the skeleton structures are made up from lines connecting two different types of stagnation points in the ABC-flow. The corresponding kinematic ABC-dynamo problem is solved using a spectral method, and the distribution of cigar-like magnetic structures visualized. Inherent links are found to exist between LCSs in the ABC-flow and induced magnetic structures, which provides insight into the mechanism behind the ABC-dynamo