The generation and evolution of heated vortex structures induced by a single-dielectric-barrier-discharge plasma actuator under burst-mode actuation are investigated in initially quiescent air using a fourth-order flux reconstruction scheme. In each burst cycle, a burst vortex forms by the rolling up of the head of the hot wall jet generated by the actuator. The burst vortex travels faster in the streamwise direction than in the wall-normal direction because it receives streamwise-dominant momentum injected by the actuator and gains additional acceleration from the induced velocity field of its adjacent downstream burst vortex. Burst vortices generated from different burst cycles ultimately merge downstream to form a large cumulative vortex, a phenomenon not previously documented. This cumulative vortex carries significantly more momentum, heat, and vorticity than the burst vortices and is believed to play a critical role in flow control. Since the cumulative vortex does not directly receive the streamwise-dominant momentum injected by the actuator, its motion shows no directional preference and its speeds in the streamwise and wall-normal directions are comparable. The burst frequency controls the spacing between adjacent burst vortices and, thereby, influences their interaction, resulting in faster streamwise motion as the burst frequency increases. However, it does not affect the size or motion of the cumulative vortex because the actuator's effective actuation duration remains unchanged. In comparison, increasing the duty-cycle ratio prolongs the actuation duration per burst cycle, generating larger vortices that carry more momentum, heat, and vorticity and move faster in both directions. These findings highlight the multi-scale vortex system generated by burst-mode actuation, which is significant for achieving more effective plasma-based flow control.
Zhao et al. (Fri,) studied this question.