A tri-electrode plasma actuator (TED-PA), which has an additional electrode with a DC voltage, induces jets from two facing electrodes and achieves larger thrust and higher efficiency than a conventional dielectric barrier discharge plasma actuator. However, there are problems such as the large potential difference between the exposed electrodes, which can cause sparks and device destruction. Therefore, it is necessary to clarify the working mechanism of TED-PAs and optimize their configuration and applied voltage. In this study, we obtained the discharge photograph, the thrust, and the flow velocity field and investigated the characteristics of the DC voltage and the frequency of the AC voltage. To isolate the effects of the discharge from the potential variation, a corona discharge plasma actuator and a TED-PA were compared. As a result, increasing the frequency of the AC voltage induced stronger jets from the AC and DC electrodes. This result indicates that the barrier discharge enhances the jet from the DC electrode without changing the potential difference between the electrodes.

The plasma actuator is an active flow control device utilizing the atmospheric dielectric barrier discharge. It has many advantages, and it is expected to be applied to a number of fluidic machines including enhancement of convection cooling. However, there is a significant problem when we apply the plasma actuator in the field of cooling, that is the actuator itself is a heat generation source due to the discharge. Although some research efforts have been devoted to understanding the heating characteristics of the plasma actuators, they made discussions only on the surface temperature, and any quantitative discussions on the amount of heating to the dielectric were not performed. The purpose of this study is to quantitatively discuss the heat transfer to the dielectric surface of the plasma actuator. For this purpose, the heat transfer coefficient and temperature of the wall-surface jet are estimated by applying it to a theoretical solution of the one-dimensional heat conduction inside the actuator. The time variation of temperature of the dielectric surface is measured using the IR camera. As a result, the estimation was reasonable near the electrode edge, but unphysical values were obtained downstream because of the small temperature rise and two-dimensional heat conduction in the dielectric. In the future, we need to analyze considering two-dimensional heat conduction utilizing numerical calculation.

Dielectric barrier discharge plasma actuators (DBDPAs) have been investigated for active flow control. The discharge induces ionic wind, which can be utilized for flow control; however, it simultaneously heats the flow and the dielectric surface. The thermal characteristics of the DBDPA must be clarified for applications in thermo-fluid engineering, such as forced convective cooling. In this study, we constructed a similarity law for the time variation of the surface temperature, assuming that the induced flow was heated by the discharge and that the dielectric was heated by the airflow. The similarity law was derived from the one-dimensional heat conduction equation in the dielectric, and the spatially averaged normalized temperature was then formulated as a function of the Biot and Fourier numbers. To experimentally validate the similarity law, the surface temperature, thrust, and power consumption were measured. The induced flow temperature and heat transfer coefficient were estimated based on the thrust and power consumption. The measured results verified that the similarity law was valid, regardless of the dielectric material, thickness, or applied voltage. This result supports the hypothesis regarding the heating mechanism in which the airflow is heated by Joule heating and the dielectric is heated by forced convection.

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