The term plasma actuator has now been a part of the fluid dynamics flow-control vernacular for more than a decade. A particular type of plasma actuator that has gained wide use is based on a single–dielectric barrier discharge (SDBD) mechanism that has desirable features for use in air at atmospheric pressures. For these actuators, the mechanism of flow control is through a generated body-force vector field that couples with the momentum in the external flow. The body force can be derived from first principles, and the effect of plasma actuators can be easily incorporated into flow solvers so that their placement and operation can be optimized. They have been used in a wide range of internal and external flow applications. Although initially considered useful only at low speeds, plasma actuators are effective in a number of applications at high subsonic, transonic, and supersonic Mach numbers, owing largely to more optimized actuator designs that were developed through better understanding and modeling of the actuator physics. New applications continue to appear through a growing number of programs in the United States, Germany, France, England, the Netherlands, Russia, Australia, Japan, and China. This review provides an overview of the physics and modeling of SDBD plasma actuators. It highlights some of the capabilities of plasma actuators through examples from experiments and simulations.

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We present simultaneous optical, electrical, and thrust measurements of an aerodynamic plasma actuator. These measurements indicate that the plasma actuator is a form of the dielectric barrier discharge, whose behavior is governed primarily by the buildup of charge on the dielectric-encapsulated electrode. Our measurements reveal the temporal and macroscale spatial structure of the plasma. Correlating the morphology of the plasma and the electrical characteristics of the discharge to the actuator performance as measured by the thrust produced indicates a direct coupling between the interelectrode electric field (strongly modified by the presence of the plasma) and the charges in the plasma. Our measurements discount bulk heating or asymmetries in the structure of the discharge as mechanisms for the production of bulk motion of the surrounding neutral air, although such asymmetries clearly exist and impact the effectiveness of the actuator.

An atmospheric-pressure dielectric barrier discharge (DBD) plasma, operated as a surface-mode discharge with a single encapsulated electrode and an asymmetric electrode alignment, is known to couple momentum into the surrounding neutral fluid and through this coupling has shown considerable promise as an aerodynamic flow control device. Several different models, often with conflicting explanations, have been offered to explain the process of this momentum coupling. The DBD is known to proceed in two stages during the discharge cycle, one on the positive-going portion of the applied ac high-voltage waveform and the other on the negative-going portion. By using the actuator to drive a second-order mechanical system, we show here that the great majority (97%) of the momentum coupling occurs during the negative-going portion of the discharge cycle and we relate this behavior to dramatic differences in the structure of the discharge revealed with high-speed photography. This information is critical in evaluating descriptions of the momentum-coupling processes in the plasma.

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