Control of unsteady flow separation over a circular cylinder using dielectric-barrier-discharge surface plasma

Dielectric-barrier-discharge plasma actuators have been used to control the unsteady flow separation over a circular cylinder at Re=15 000 with a view to maximizing the lift with a minimum drag increase. The flow structure was studied using time-resolved particle image velocimetry and flow visualization, while the dynamic lift and drag were simultaneously measured with a two-component force balance. Our results show that the lift can be dramatically increased by a single, short-duration pulse of plasma at carefully chosen location and timing. A peak lift coefficient of 1.24 was observed, showing that the plasma can increase lift by over 300%, with less than 25% increase in drag. Optimal conditions occurred when the actuator was located at 75 degrees from the streamwise axis, with plasma forcing timed to coincide with the retreat of the separation point. This corresponds to the actuator being located 7 degrees upstream of the natural separation point. The peak lift was relatively insensitive to the duration of the plasma.