1478 IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 38, NO. 6, NOVEMBER/DECEMBER 2002 Effect of a DC Corona Electrical Discharge on the Airflow Along a Flat Plate Luc Léger, Eric Moreau, and Gérard G. Touchard Abstract—Ability of a dc electrical discharge to control low-ve- locity airflow along a flat plate is analyzed. Specifically, the elec- trodes are flush mounted on the insulating surface of the plate cre- ating a tangential corona discharge at close vicinity of the wall. In this paper, visualizations of the low-velocity airflow (up to 1.4 m/s corresponding to ) along the flat plate are presented. They show that the ionic wind induced by the corona discharge modifies the original airflow considerably, resulting in the airflow reattachment to the wall and reduction of the wake size. Velocity measurements by particle imaging velocimetry and by Pitot tube are conducted in a wind-tunnel loop for higher airflow velocities (up to 11 m/s corresponding to ). Results show that the corona discharge at such high airflow velocities does affect sig- nificantly the velocity profile within the viscous boundary layer. Index Terms—Airflow, corona discharge, electrohydrodynamic, flat plate, flow control. I. INTRODUCTION W HEN a dc high voltage is applied between two electrodes in air, ions may be produced at the electrode with the lower curvature radius. In their drift motion from the injection electrode to the collecting one under the effect of Coulombian forces, these ions exchange momentum with the neutral fluid particles and induce fluid movement. The fluid motion induced by the dc corona discharge is usually called electric wind or ionic wind. This electrical effect has been widely studied for its appli- cations in electrostatic cooling or electrostatic precipitation [1]–[3]. In an electrostatic precipitator, the goal is to charge particles and to collect them. There is creation of a secondary electrohydrodynamic flow, which may be used to increase effectiveness [1]. Corona discharge may be used in order to increase heat transfer. For example, several authors showed that an ionic wind might increase heat transfer as much as 200% [2], [3]. Corona discharge may be also used to modify airflow around an obstacle. This is referred to as “electroaerodynamics.” Very limited work has been published on this subject [4]–[18]. The main advantage of this process is that it directly converts elec- tric energy into kinetic energy, without moving mechanical part. Paper MSDAD-A 02–24, presented at the 2001 Industry Applications So- ciety Annual Meeting, Chicago, IL, September 30–October 5, and approved for publication in the IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS by the Electrostatic Processes Committee of the IEEE Industry Applications Society. Manuscript submitted for review October 15, 2001 and released for publication August 26, 2002. The authors are with the Electrohydrodynamic Group, Laboratoire d’Etudes Aérodynamiques, UMR 6609 CNRS, University of Poitiers, 86962 Futuroscope, France (e-mail: Luc.Leger@lea.univ-poitiers.fr; eric.moreau@lea.univ-poitiers.fr; Gerard.Touchard@lea.univ-poitiers.fr). Digital Object Identifier 10.1109/TIA.2002.804769 Fig. 1. Schematic representation of the electrohydrodynamic actuator. Its objective is to accelerate the airflow tangentially and very close to the wall, in order to modify the airflow profile inside the boundary layer (Fig. 1). This process might be used to control the laminar-turbulent transition inside the boundary layer, to re- duce the drag of a plane wing, or to stabilize the flow in order to avoid unsteadiness which generates unwanted vibrations, noise, and losses. Ionic wind has been widely studied in the case of a corona discharge between a needle and plate electrode in stagnant free gas. Yabe et al. [4] and Ballereau [5] observed that the velocity of the corona wind increases with the square root of the current. However, studies with electrodes flush mounted on an insulating surface have received less attention. Velkof et al. [6] demonstrated that the transition point on a flat plate could be affected by the application of an electric field. They observed a downstream shift of the transition loca- tion. Bushnel [7] and Malik et al. [8] reported an ionic wind of several meters per second contributing to drag reduction. Van Rosendal and Malik [9] studied Poiseuille flow at low velocity and found that skin-friction distribution was strongly affected by the presence of ionic wind. They showed numerically a drag reduction with an order of magnitude of 20%. Soetomo [10] ex- perimentally observed a drag reduction effect induced by ac and dc corona discharges along a flat plate in the case of flow ve- locities up to 2 m/s. Considering the same experimental condi- tions, Colver and El Khabiry [11] numerically showed a con- sistent drag reduction. However, these studies were limited to low-velocity airflows (some meters per second). In a previous study [12], we observed an important reduction of the wake downstream an inclined flat plate for velocities of some meters per second. Particles imaging velocimetry (PIV) experiments showed a high acceleration of the airflow downstream from the discharge. Analysis of the flow streamlines indicated that the discharge resulted in reattachment of the airflow to the wall. More PIV experiments for faster airflows (from 10 to 20 m/s) 0093-9994/02$17.00 © 2002 IEEE