Flow around a circular cylinder controlled by asymmetric plasma actuation

The flow field over a circular cylinder with a pair of dielectric-barrier-discharge (DBD) plasma actuators under steady and unsteady actuation in quiescent air is simulated by solving the Navier-Stokes equations. During the duty cycle actuation, duty cycle ratio determines the fraction of time when the left actuator is turned on during a duty cycle period T=1/f, where f is the duty cycle frequency. When the left actuator is turned on, the right actuator is turned off and vice versa. Under this actuation, vortices are generated alternately from each side of the cylinder. The present study focuses on the detailed flow structure including the wall jets, the evolution of vortices, and the resultant momentum of the flow induced by the DBD actuators in order to gain more insight into flow control mechanisms under different types of actuation. Simulations are performed for f ranging from 5Hz to 100Hz and duty cycle ratio from 0.3 to 0.7. For low duty cycle frequencies, a pair of discrete vortices are generated in each actuation cycle. They interact and move downstream in response to the on-off signals of the actuators. As the frequency increases, the distance between vortices from successive duty cycles decreases so that the vortices are packed together as a vortex train along a narrow path line. As the frequency further increases, the vortices in the train lose their individual characteristics and the vortex trains become two jets, one on each side of the cylinder.