Surface dielectric barrier discharge: Effect of encapsulation of the grounded electrode on the electromechanical characteristics of the plasma actuator Jean-Charles Laurentie, Je ´ro ˆme Jolibois, Eric Moreau * Laboratoire d’Etudes Ae´rodynamiques (LEA), University of Poitiers, ENSMA, CNRS, Bld Marie et Pierre Curie, Teleport 2, 86962 Futuroscope, France article info Article history: Received 26 September 2008 Received in revised form 1 January 2009 Accepted 18 January 2009 Available online 15 February 2009 Keywords: Dielectric barrier discharge Plasma actuator Electric wind Discharge current Streamers abstract Active flow control is a rapidly developing topic because the associated industrial applications are of immense importance, particularly for aeronautics. Among all the flow control actuators, plasma-based devices are very promising. In most cases, the plasma actuator is based on a surface dielectric barrier discharge (DBD) established between two electrodes flush mounted on both sides of a dielectric layer. In this paper, the effects of the encapsulation of the grounded electrode on the electric wind produced by a surface DBD are investigated by Pitot velocity measurements. Moreover, the current versus time is statistically analysed in order to count the number of streamers, their duration and the electrical charge they transfer. Unfortunately it was not possible to detect and separate the glow-type synchronous current because its amplitude is of the same order as noise. On one hand, the encapsulation of the grounded electrode results in an increase of the electromechanical efficiency of the surface DBD plasma actuator because the electrical power consumption is divided by two. On the other hand, statistical analysis of the discharge current versus time has shown that the encapsulation results in a decrease of the streamer number and an increase of the charge transferred by each current streamer because the duration of streamers is longer. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction Many studies have shown that surface discharges may be used as an air-moving actuator for airflow control [1–5]. The main advantages of these actuators are their low weight and their ergonomics. The mechanical effect of such actuators is the produced electric wind, which is due to the migration of ions inside plasma. Many studies on the Dielectric Barrier Discharge (DBD) actuator have been conducted in order to improve its mechanical performance and to decrease its electrical power consumption in the absence of airflow [6–8]. This study is focused on this objective. The DBD plasma actuator usually consists in two electrodes flush mounted on both sides of a dielectric layer. Then two plasmas are produced on each side of the dielectric plate. Both plasmas produce electric wind, but usually only one is used. Removing the needless plasma is an effective way to reduce the electrical power consumption. A solution is to encapsulate one of both electrodes in a dielectric material in order to avoid the plasma discharge on one side of the dielectric layer. The present study is dedicated to the characterization of the encapsulation effects. First, an electromechanical study is conducted for a high voltage ranging from 12 kV to 21 kV at 1 kHz. The time-averaged velocity of the electric wind produced by the surface discharge is measured with the help of a Pitot tube. Then the resulting mechanical power, the electrical power consumption and the actuator electromechanical efficiency are investigated. Secondly, the current versus time is statistically analysed. At the beginning of this study, our ultimate goal was to detect and separate the four components of the measured current, i.e. the capacity component, the synchronous component, the pulse component and noise. Unfortunately, although it is well known that it plays a major role in the surface DBD electric wind production [9], it was not possible to estimate and isolate the glow-type synchronous current because its amplitude was too small and similar to the noise magnitude. Consequently, the statistical analysis of the discharge current is limited here to the pulse current, which is easier to detect. The number of streamers, their duration and the electrical charge they transfer will be computed. 2. Experimental set-up Here the single DBD plasma actuator is composed of two elec- trodes flush mounted on both sides of a 3-mm-thick PMMA dielectric sheet. Both electrodes are made of aluminium strips. They are 20 mm wide and 150 mm long. The gap between the side of each * Corresponding author. E-mail address: eric.moreau@lea.univ-poitiers.fr (E. Moreau). Contents lists available at ScienceDirect Journal of Electrostatics journal homepage: www.elsevier.com/locate/elstat 0304-3886/$ – see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.elstat.2009.01.056 Journal of Electrostatics 67 (2009) 93–98