Core of the Magnetic Obstacle

TL;DR

This study investigates the core of magnetic obstacles in conducting flows under strong magnetic fields, revealing streamlined flow patterns, new recirculation structures, and the 'frozen' nature of the obstacle core through advanced simulations.

Contribution

It provides new insights into the structure and behavior of magnetic obstacle cores, including the discovery of novel recirculation patterns and the analogy between flow and electric potential contours.

Findings

Core of magnetic obstacle is streamlined by flow and electric currents.

New recirculation vortices are identified in 2D simulations.

Core remains 'frozen' with vortex intensities vanishing at the center.

Abstract

Rich recirculation patterns have been recently discovered in the electrically conducting flow subject to a local external magnetic termed "the magnetic obstacle" [Phys. Rev. Lett. 98 (2007), 144504]. This paper continues the study of magnetic obstacles and sheds new light on the core of the magnetic obstacle that develops between magnetic poles when the intensity of the external field is very large. A series of both 3D and 2D numerical simulations have been carried out, through which it is shown that the core of the magnetic obstacle is streamlined both by the upstream flow and by the induced cross stream electric currents, like a foreign insulated insertion placed inside the ordinary hydrodynamic flow. The closed streamlines of the mass flow resemble contour lines of electric potential, while closed streamlines of the electric current resemble contour lines of pressure. New recirculation patterns not reported before are found in the series of 2D simulations. These are composed of many (even number) vortices aligned along the spanwise line crossing the magnetic gap. The intensities of these vortices are shown to vanish toward to the center of the magnetic gap, confirming the general conclusion of 3D simulations that the core of the magnetic obstacle is frozen. The implications of these findings for the case of turbulent flow are discussed briefly.