Spatiotemporal structure of a millimetric annular dielectric barrier discharge plasma actuator

The spatiotemporal structure of a millimetric annular dielectric barrier discharge plasma actuator is investigated using a photomultiplier tubea high-sensitivity cameraparticle image velocimetryelectrohydrodynamics simulations. Plasma actuators have typically demonstrated their utility in flow separation controlbut on a millimetric scale they have also shown to be promising in the control of crossflow instabilities in crossflow-dominated laminar-turbulent boundary-layer transition. In view of the subtleties associated with creating an initial disturbance to excite subcritical wavelengthsit is desirable to characterize the local plasma discharge structurebody force organizationinduced velocity field in detail. The results show thatsimilar to their linear centimetric counterpartthe plasma discharge has a highly dynamic and somewhat organized spatiotemporal structure. Under quiescent flow conditionsthe actuator induces a velocity field that consists of two counter-rotating vorticesaccompanied by a wall-normal synthetic jet regionwhich in three-dimensions describes a toroidal vortex around the apertures periphery. The surprising resulthoweveris that these vortices rotate in the opposite direction to vortices generated by similar centimetric annular designs. Three-dimensional electrohydrodynamics simulations correctly reproduce this behavior. Because the body force organization may be qualitatively perceived as being the axisymmetric counterpart of the more classical linear actuatorthis flow reversal is thought to be due to the actuator scale. When an array of millimetric actuators is considered in close proximityan interaction takes place between the vortices created from each actuator and those of neighboring actuatorsresulting in a significant reduction in vortex size compared with the single aperture caseaccompanied by an increase in the maximum induced flow velocity magnitude.