Autonomous Sensing and Control of Wing Stall Using a Smart Plasma Slat

The concept of a self-governing smart plasma slat for active sense and control offlow separation and incipientwing stall is presented. The smart plasma slat design involves the use of an aerodynamic plasma actuator on the leading edge of a two-dimensional NACA 0015 airfoil in a manner that mimics the effect of a movable leading-edge slat of a conventional high-lift system. The self-governing system uses a single high-bandwidth pressure sensor and a feedback controller to operate the actuator in an autonomous mode with a primary function to sense and control incipient flow separation at the wing leading edge and to delay incipient stall. Two feedback control techniques are investigated. Wind tunnel experiments demonstrate that the aerodynamic effects of a smart actuator are consistent with the previously tested open-loop actuator, in that stall hysteresis is eliminated, stall angle is delayed by 7 deg, and a significant improvement in the lift-to-drag ratio is achieved over a wide range of angles of attack. These feedback control approaches provide a means to further reduce power requirements for an unsteady plasma actuator for practical air vehicle applications. The smart plasma slat concept is well suited for the design of low-drag, quiet, high-lift systems for fixed-wing aircraft and rotorcraft. Nomenclature CL = coefficient of lift CL;max = maximum coefficient of lift c = airfoil chord length F = nondimensional frequency of actuator f = modulation frequency of actuator L=D = ratio of lift to drag Lsep = extent of flow separation Re = Reynolds number Rechord = Reynolds number based on length c