Reversed steady streaming generated by a free-moving magnet.*

Steady streaming is produced using a small magnet that oscillates due to electromagnetic forcing. The magnet is kept afloat on a shallow layer of weak conducting electrolyte. The oscillatory motion is promoted by injecting an alternating electric current to the electrolyte, the current interacts with the magnetic field of the magnet generating a Lorentz force in the fluid whose motion drives the magnet. In our case study, the well-known vortical structures of the streaming rotate in opposite direction to previous works on the subject. This reversed streaming is attributed to a non-previously considered degree of freedom, namely, the coupling between the fluid and the free-moving body. Analytical one-dimensional and two-dimensional solutions give a simple insight into the observed dynamics of the oscillating magnet and the promoted reversed streaming, respectively. A quasi-two-dimensional numerical simulation reproduces the experimental observations satisfactorily.