Measurements and simulations of surface dielectric barrier discharges used as plasma actuators

Asymmetric surface dielectric barrier discharges (DBDs) have shown promise for use as aerodynamic actuators which can prevent flow separation from airfoils in low-Reynolds number gas flow. Our DBDs used a symmetric triangular high voltage waveform to generate plasma in atmospheric pressure air. Plasma forms and decays in many nanosecond-scale microdischarges during each millisecond-scale half cycle of the applied voltage, and the device induces a time-averaged force on the nearby air. Time-averaged measurements indicated that the induced force of a single-barrier actuator design (one electrode insulated from the plasma) can be increased exponentially above the results of previous studies by decreasing both the length and thickness of the electrode exposed to the plasma. This increased force may allow these devices to control flow separation in a wider range of flow environments. Experiments using an intensified digital camera to examine the plasma on time scales of a few nanoseconds up to the applied voltage period showed that, in addition to the previously-observed filamentary and jet-like plasma structures, discharges with very thin exposed electrodes exhibited a weak but constant plasma immediately adjacent to those electrodes. In double-barrier actuators (both electrodes insulated), decreasing the diameter of the narrower electrode lead to increasing forces, and recorded images showed the simultaneous existence of both filamentary and jet-like plasma structures. The development and application of a time-dependent, two-dimensional fluid plasma model has aided in undestanding the detailed physics of surface DBDs at all time scales. For simulated single-barrier discharges, the model qualitatively reproduced the filamentary and jet-like microdischarge structures. The model was somewhat successful in reproducing the observed characteristics of double-barrier actuators. For both actuator geometries, the model indicated that the majority of the forces induced on the neutral gas occur in between microdischarges as the plasmas decay.