Aerodynamic modification of flow over bluff objects by plasma actuation

Particle image velocimetry and smoke visualization are used to study the alteration of the flow field in the wake of a bluff body by use of an alternating current (AC) surface dielectric barrier discharge. Staggered, surface, and buried electrodes were positioned on the downstream side of circular cylinders at conditions of Re-D = 1 x 10(4) -4 x 10(4) configured to impose a force due to the ion drift that is either along or counter to the free-stream flow direction. Smoke visualization and Particle Image Velocimetry (PIV) in the wake of the flow confirms that the configuration of the surface electrodes and operation of the discharge significantly alters the location of the flow separation point and the time-averaged velocity profiles in the near and distant wake. Measurements of the vibrational and the rotational temperature using optical emission spectroscopy on the N-2 second positive system (C-3 Pi(u)-B-3 Pi(g)) indicates that the resulting plasma is highly non-equilibrium and discounts the possibility of a thermal effect on the flow separation process. The mechanism responsible for reduction or enhancement of flow separation is attributed to the streamwise force generated by the asymmetric ion wind-the direction of which is established by the electrode geometry and the local surface charge accumulated on AC cycles.