Flight Testing of DBD Plasma Separation Control System

The paper deals with flight tests of dielectric barrier discharge control devices. Plasma activators were installed on sailplane’s wing and attempts to use them for control of flow separation in pre- and post- stall flight regimes were performed. Main efforts in this study were done to design plasma flow control system and develop flight test procedures. It was experimentally shown that plasma actuators can be used onboard of an aircraft as a part of control system. I. Introduction XISTING methods of flight safety improvement for near-stall flight regimes are developed in two directions: installation of stall warning devices and maintenance of controllability in post-critical regimes by means of vortex generators, automatic slats and other similar devices. Generally, the combination of these methods is applied, and each of them has its own lacks. Decrease of angle of attack after triggering of stall warning demands reasonable time and speed reserve. It could not be possible near the ground or in strong turbulence. Installation of vortex generators and other mechanical devices leads to additional drag, design complication and aircraft weight growth. Among modern adaptive methods of flow separation control, such as: blow-suction of boundary layer, synthetic jets and micro-mechanical activators, application of devices based on principle of the Dielectric Barrier Discharge (DBD) has doubtless advantages. These devices have simple design, insignificant weight and do not distort geometry of wing airfoil. The principle of DBD operation is based on additional acceleration and excitation of preseparated boundary layer by EHD force that consequently promotes delay of boundary layer separation up to higher angles of attack and changes its character. In real flight conditions it should also lead to reduction of stall speed of aircraft and to maintenance of controllability on post-stall angles of attack. Study of DBD application for separation control on wing airfoils have begun rather recently [1,2,3], but doubtless growing interest to the given subjects is observed by present time. The majority of the experimental studies executed by present time have been performed at low free stream speeds (up to 10 m/s) or with small airfoil models. Therefore, the questions of scaling and possibility of practical application of DBD devices for flow separation and stall control in real flight conditions remain opened. The team of Institute of Theoretical and Applied Mechanics have experience of application of DBD and other plasma discharges for flow separation control [4,5,6]. Recent experiments in wind tunnel Т-324 made with 1m span models of straight and swept wings have testified that the method is ready for approbation in real flight condition experiments. The transfer of such new technology as DBD control system from wind tunnel environment to a real aircraft is complex problem and flight experiments have to answer several important questions about practical realization and possibilities of DBD for flight control. First of all we have to try to develop high-voltage generator / plasma actuator system which is suitable for installation onboard of an aircraft from point of view of weight, power and efficiency. If such system would be designed it has to be safe in operation or special procedures have to be implemented. DBD control systems deal with RF plasma sources of significant power so practical questions such as radio-electronic emission, electrical safety and reliability of system have to be studied. The perspective goal of the project is application of DBD for maintenance of controllability of the aircraft in post-stall range of angles of attack. The purpose of current flight tests is to investigate all practical sides of DBD application mentioned above as well as to study DBD effect on flow separation on the wing in near-stall envelope of the angles of attack.