Electromagnetically driven oscillatory shallow layer flow

We report experimental observations of the laminar flow in a thin horizontal layer of electrolyte, generated by a time-periodic Lorentz force produced by an alternate, unidirectional electric current and the field of a small permanent magnet. The force drives a periodically oscillating dipolar vortex which displays some spatial and temporal symmetries. The attention is focused on the motion of the oscillatory layer in vertical planes perpendicular to both the bottom wall and the injected current. For different frequencies of the injected current, velocity fields were obtained using particle image velocimetry in the zone of more intense magnetic field as well as close to the edges of the magnet where the inhomogeneity of the field is more pronounced. Velocity profiles as functions of the normal coordinate are determined in characteristic points at different phases and oscillation frequencies. Experimental results are compared with a simple analytical solution and a full three-dimensional numerical simulation that reproduces satisfactorily the experimental observations. Under the explored conditions and available experimental resolution, results indicate that except in the zone above of the lateral edges of the magnet, no recirculating flows appear and vertical velocity components are negligible. (c) 2011 American Institute of Physics. [doi:10.1063/1.3531729]