Feedback Control for Laminarization of flow over Wings

An active control strategy is implemented to attenuate the amplitude of the Tollmien-Schlichting (TS) waves inside the boundary layer of an airfoil. The dynamics of the system are modelled by the linearised Navier-Stokes equations. The impulse response to an initial disturbance, initially located outside of the boundary layer and in front of the airfoil is considered. The perturbation evolves and penetrates inside the boundary layer and triggers the TS waves. Different control strategies including the linear quadratic Gaussian (LQG) and model predictive control (MPC) are designed based on a reduced order model where the sensors and actuators are localised near the wall. An output projection is used to identify the unstable disturbances; the objective function of the controller is selected as a set of proper orthogonal decomposition (POD) modes; to isolate the dynamics of the TS waves, the modes with high energy contents in the TS wave frequency band are considered as the objective of the controller. A plasma actuator is modelled and implemented as an external forcing on the flow. To account for the limitations of the plasma actuator several strategies are examined and the results are compared with a classical LQG controller. The outcomes reveal successful performance in mitigating the amplitude of the wavepacket developing inside the boundary layer.