Wake patterns behind a magnetic obstacle in an electrolyte layer

J. Román¹ - A. Figueroa² - S. Cuevas¹

¹ Instituto de Energ\'ias Renovables, Universidad Nacional Autónoma de México, Temixco, Morelos, 62580 México
² CONACYT-Centro de Investigación en Ciencias, Universidad Autónoma del Estado de Morelos, Cuernavaca, Mor. 62209, México

Abstract
We present an experimental study of vortex wakes produced by a travelling localized Lorentz force in a thin layer of electrolyte. The fluid is contained in an open rectangular channel with two parallel electrodes placed along the longest walls so that a uniform DC current is supplied through the layer. A permanent magnet located under the container is moved with a constant velocity so that the interplay of the moving magnetic field and the applied transversal current generates a Lorentz force. The variation of the applied current and the velocity of the magnet leads to different vortex patterns, such as jet-like flow, travelling vortex dipole, Bénard-von Kármán wake and 2P wake, which are visualized by tracers and analyzed using Particle Image Velocimetry. The flow is governed by the Reynolds number based on the velocity and size of the travelling magnet and by the Chandrasekhar number based on the applied current. An experimental map characterizing different flow patterns and the transition among them is built in terms of these parameters. Numerical results using a quasi-two-dimensional model reproduce the main features observed in the experiments. Figs 11, Refs 16.