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Several wind-tunnel experiments shall demonstrate the possibility of active subsonic separation flow control in weakly ionized air. The partially air plasma around insulating and conducting test bodies (cylinder, fuselages, wings, blades, propellers) will be generated by different kind of plasma actuators (corona wires, silent surface discharges from plastic and ferroelectric ceramic film layers etc.) which are capable to energy-efficiently generate and maintain atmospheric pressure air plasmas.

Active Separation Flow Control Using Plasma Actuators

Pictures:  In 2004 subsonic separation flow control experiments with an Eppler E338 airfoil 2D-wing using phased dielectric barrier discharge plasma actuators.

Pictures:  In 2005 subsonic separation flow control experiments with an Eppler E338 airfoil 3D-wing using phased dielectric barrier discharge plasma actuators.

Pictures:  In 2005 subsonic separation flow control experiments with an Eppler E338 airfoil flying wing half model using phased dielectric barrier discharge plasma actuators.

Pictures:  First subsonic separation flow control experiments by means of electric field actuation started in 1999 and were sponsored by FESTO AG.

High voltage electrostatic gas discharges from a spanwise corona wire placed 2.5 cm in front of the conducting leading edge of a dielectric wing with 50 cm span width were applied to control the separation in low Reynolds number air flows in two low speed free-jet wind-tunnels. Additional discharge electrodes acting as plasma flaps were placed on the upper surface of the rectangular wing to energize the boundary layer through ionic winds. Plexi glas end discs were used to maintain a two-dimensional flow for visualization and measurement of aerodynamic forces with a two component balance. The chord Reynolds number range was from 6,500-130,000 which equals a velocity range from 0.5 - 11 m/s (0,5 - 6,6 and 6,6 - 11 m/s) typical for micro aerial vehicle. The average electrical power expenditure is 8 Watt per 50 cm corona wire positively charged with 16 – 17 kV with a maximum current limited by the high voltage power supply to 0.5 mA.

The influence of unipolar space charges on boundary-layer separation was visualized with continous smoke generated from a hot wire placed in front of the wing leading edge but perpendicular to the span width to provide a cross-sectional view of the flow field. Laser light sheet techniques were used to illuminate the fine paraffin oil smoke.

The flow visualizations at different velocities illustrate the results of the lift diagrams showing dramatic separation delays and resulting lift enhancement by applying electrostatic forces for a very modest expenditure of energy. Video recordings with different camera views clearly show the strong and reproducible flow modifications around the airfoil at high angles of attack up to 30 degrees. The separated boundary-layer on the airfoil is completely corrected after switch-on of the electrostatic field leading to weakly ionized air flow.  

Recent wind-tunnel experiments with the same test wing with Eppler E338 airfoil could even demonstrate electroaerodynamic separation flow control with electrical power expenditure in the range of only 0.5 to 3 Watts at constant high voltage values of 10 kV, 12 kV, 15 kV. These values correspond with the high voltage outputs of miniaturized off-the-shell power supplies made by EMCO (see also project folder Micro Aerial Vehicle.

See for detailed results in the recent publication "Wind-Tunnel Experiments to Active Flow Control at Low Re-Numbers" presented at the First European Micro Air Vehicle Conference and Flight Competition EMAV 2004, Braunschweig, Germany.

Pictures:  Subsonic separation flow control experiments in the small free-stream wind-tunnel of the Institute of Bionics and Evolutiontechnique (2004).

Pictures:  Lift and drag diagrams at low Reynolds numbers (click on picture to see all diagrams).