Control of Natural Tollmien-Schlichting Waves using Dielectric Barrier Discharge Plasma Actuators

An experimental investigation on active control of naturally occurring Tollmien-Schlichting (TS) instabilities on a NACA 0012 airfoil is presented. A real-time closed-loop control system has been implemented using the filtered-x Least Mean Squares (FXLMS) adaptive algorithm based on Finite Impulse Response (FIR) filters. Two surface mounted microphones provide the unsteady surface pressure measurements, which are used as reference and error signal, respectively. The controller directly drives a Dielectric Barrier Discharge plasma actuator positioned on the suction side of the airfoil. In contrast to the conventionally modulated sinusoidal signal, the actuator is powered using a signal continuously adapted in real time by the controller. In this manner, the inherently unsteady plasma force production is capitalised in order to dampen the incoming wave-train of Tollmien-Schlichting instabilities. Time-resolved two-component Particle Image Velocimetry is used to characterize the flow in the vicinity of the a...