Classification of flow-field patterns in burst-mode actuation of a dielectric-barrier-discharge plasma actuator

This study investigates the characteristics of flow-field patterns generated by burst-mode actuation of a dielectric-barrier-discharge plasma actuator in quiescent air. Particle-image velocimetry and background-oriented schlieren measurements conducted over a wide range of burst-signal parameters show that there are three types of flow-field patterns. Type 1 is the wall-surface jet seen in continuous mode actuation; type 2 features periodical independent vortices traveling along the wall surface; type 3 features such vortices moving away from the surface. The vortex sizes in types 2 and 3 are proportional to the energy consumed in generating one vortex. When the time-averaged jet velocity estimated by the power consumption is used as the characteristic velocity in the nondimensional scaling law, the time profiles of the vortex location in the type 3 flow-field pattern collapse into a single line, independently of the burst frequency and ratio. However, in the initial phase, the nondimensional vortex-core motion is better described using the jet velocity in continuous-mode actuation as the characteristic velocity. The transitions of the flow-field pattern from type 1 to type 3 result from interference between cyclically generated vortices and depend on the inter-vortex distances and the energy consumed in generating one vortex.