The level of the skin friction drag depends on the boundary layer state, either low, for the laminar case or high for the turbulent case. Flow control is sought to attenuate the streamwise velocity streaks preceding sub-critical bypass transition to turbulence. In addition, the targeted instability is ubiquitous to the self-sustaining wall-bounded turbulence cycle and at the root of the long-term goal of turbulence control. The longer spatial and temporal scales associated with the laminar case make a physical demonstration of a model-based boundary layer flow control more tractable.

The effectiveness of control systems is inherently linked to the ability of the actuator to alter the flow to a desired state. Therefore, actuators are a critical enabling technology component in any active flow control system. Arguably, the most important missing technology in boundary layer flow control is effective and robust actuators, which can be readily integrated with an active flow control system. Plasma actuators fulfil these characteristics and are an ideal candidate for the control of the bypass transition instability.

In this thesis, the receptivity of the boundary layer to forcing by arrays of plasma actuators capable of producing streamwise streaks was characterized. Following, the transient growth instability was targeted in an open-loop framework to identify the physics of the attenuation mechanism, which was shown to be a linear process. The control loop was then closed with feedback from simultaneous spanwise distributed shear stress sensors. A wavenumber specific control objective was used to demonstrate the effectiveness of feedback for steady disturbance attenuation as well as to provide robustness to off-model conditions. For all cases, the targeted disturbance was reduced by over 94% of its initial energy. The control effectiveness was also validated for quasi-steady forcing by varying the input disturbance level. Ultimately, control of transient growth due to unsteady stochastic excitation is sought, and the dynamic response of the flow to pulsed actuation was studied to support the natural next step in the greater efforts of which this thesis is a critical component.