Flow around Rudder Controlled by Electromagnetic Body Force

The experiments concerning the flow around flat rudder controlled by streamwise and spanwise Lorentz force are conducted. The rudders are surface-mounted with the actuator with interlaced electrodes and magnets, and immerged into low-conducting electrolyte, such as seawater. Due to the interaction between a magnetic field and a current density, the fluid motion is induced by utilizing the Lorentz force. Two types of actuators are investigated to obtain the control effects of Lorentz force with different distribution. One actuator utilizes the streamwise Lorentz force to modify the laminar boundary layer, and qualitative analysis in the flow field and the lift and drag force is carried out. The other actuator allows the Lorentz force to be propagated in the spanwise direction, leading to a modification of the near-wall activities in the turbulent boundary layer. The control effects on the turbulent skin friction are measured using a direct measurement of drag. Substantial drag reduction by spanwise oscillatory Lorentz force is found and the relation between the amplitude of drag reduction and the oscillation period of the Lorentz force is also discussed.