The starting vortex in quiescent air induced by dielectric-barrier-discharge plasma

The flow field around an asymmetric dielectric-barrier-discharge (DBD) plasma actuator in quiescent air is studied using particle image velocimetry (PIV) and smoke-flow visualization. On initiation of DBD plasma a starting vortex is created, which rolls up to form a coherent structure. The starting vortex becomes self-similar when the maximum velocity induced by the DBD plasma actuator reaches a steady state. Here, the plasma jet momentum increases linearly with time, suggesting that the DBD plasma actuator entrains and accelerates the surrounding fluid with a constant force. The wall-parallel and wall-normal distances of the vortex core are observed to scale with ${t}^{2/ 3} $ as it travels at $3{1}^{\circ } $ to the wall. The velocity of the starting vortex is found to scale with ${t}^{- 1/ 3} $, while the circulation induced by the plasma actuator scales with ${t}^{1/ 3} $.