Control of a separating boundary layer with Lorentz force actuators

The effect of time-periodic spanwise Lorentz forces on flow separation in a weakly conductive fluid is examined. An array of alternately arranged electrodes and permanent magnets constituted an electromagnetohydrodynamic actuator, which was flush mounted on a hydrofoil model with a flap that was inclined at 20° to the freestream flow in a water tunnel. Above a certain amplitude of electromagnetohydrodynamic forcing, complete reattachment of flow over the flap was seen from measured velocity fields by using particle image velocimetry. It is proposed that introduction of streamwise vorticity generated by the spanwise Lorentz forces into the flow field over the actuator surface is responsible for the reattachment of flow.