Spatiotemporal structure of a millimetric annular dielectric barrier discharge plasma actuator

Abstract

The spatiotemporal structure of a millimetric annular dielectric barrier discharge plasma actuator is investigated using a photomultiplier tube, a high-sensitivity camera, particle image velocimetry, and electrohydrodynamics simulations. Plasma actuators have typically demonstrated their utility in flow separation control, but 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 wavelengths, it is desirable to characterize the local plasma discharge structure, body force organization, and induced velocity field in detail. The results show that, similar to their linear centimetric counterpart, the plasma discharge has a highly dynamic and somewhat organized spatiotemporal structure. Under quiescent flow conditions, the actuator induces a velocity field that consists of two counter-rotating vortices, accompanied by a wall-normal synthetic jet region, which in three-dimensions describes a toroidal vortex around the aperture's periphery. The surprising result, however, is 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 actuator, this flow reversal is thought to be due to the actuator scale. When an array of millimetric actuators is considered in close proximity, an interaction takes place between the vortices created from each actuator and those of neighboring actuators, resulting in a significant reduction in vortex size compared with the single aperture case, accompanied by an increase in the maximum induced flow velocity magnitude.

Plasma virtual roughness elements for cross-flow instability control

“…The flow around a ring-type actuator was seen accelerated towards the lower electrode and spread out in the radial directions, confirming the results by Humble et al (2013). It showed necklace vortices as well as secondary vortices over the ring-type plasma actuator, but without additional vorticity region on top.…”

“…Ring-type plasma actuators of 3-mm aperture diameter were investigated by Humble et al (2013) for controlling cross-flow dominated boundary layer. The actuators consisted of upper electrodes made of etched gold-plated copper, which were attached to 0.5-mm-thick polyimide dielectric sheets.…”

“…The streamwise vorticity associated with this flow field is shown in Fig. 14. The ring-type plasma actuators with small diameter (d ≲ 5 mm) induce wall-normal flow towards the centre of the actuator (Humble et al 2013), therefore the flow around this ring-type actuator is accelerated towards the lower electrode and spread out in the radial directions. This is displayed in Fig.…”

Modeling and theoretical analysis of SDBD plasma actuators driven by Fast-Rise-Slow-Decay Pulsed-DC voltages

“…When the high-voltage pulses are shorten to tens or hundreds of nanoseconds, a micro perturbation wave will be generated near the high-voltage electrode due to fast gas heating by the quenching of electronically excited states [7][8][9][10][11]. The features of ionic wind generation and fast gas heating are essential in separation flow control [12][13][14], boundary-layer transition control [15,16] and skin-friction reduction in boundary/mixing layer [17][18][19][20] et al…”

Localized micro-discharges group dielectric barrier discharge vortex generators: Disturbances source for active transition control

“…Although this configuration was studied experimentally rather well, the down scaling of the system dimensions was shown to be a complex one. For example, it was shown 10 that when the electrode diameter is reduced down to several millimeters, the flow generated on the actuator axis changes its sign and it begins to work as a suction device rather than a blowing one.…”