Investigation of wall normal electromagnetic actuator for seawater flow control
Résumé
Electromagnetic (EM) flow control deals with the concept of using in combination ‘wall-flush’ electrodes ( j , dc current supply) and ‘sub-surface’ magnets ( B , magnetic induction origin) to create directly local body forces ( j × B ) within a seawater boundary layer. Analytical, experimental and computational investigations of EM flow control are presented here. This work is intended to provide understanding of the basic mechanisms involved in turbulence intensity and skin friction reductions as well as in coherent structure extinction. First, the EM actuator and its modes of action are described. This description includes some general remarks on the EM actuator, the set of equations suitable for EM control in seawater and a selection of dimensionless parameters analysed in terms of possible mechanisms of action. Second, some experimental investigations and visualizations of wall-bounded flows under EM actuation are presented: the near-wall vortex around the actuator; the suction zone above the actuator; wall jets around the actuator and boundary layer ‘suction-blowing’.