Active Boundary Layer Control: An Experimental Investigation in Turbulent Boundary Layer Skin-Friction Drag Reduction Using Pulsed DC Plasma Actuators

Viscous drag reduction is a much researched topic in turbulent boundary layer theory dating back to the 1950s. Decades of both experimental and computational research has uncovered numerous effective techniques that produce a net reduction in viscous drag. The variety of methods utilized in reducing viscous drag, applying both passive and active flow control techniques, have greatly increased the understating of the physical nature and complexity of the turbulent boundary layer mechanisms. The work presented in this dissertation is intended to contribute to this strong research foundation by demonstrating the capability of one such method, providing an insightful understanding of the complex dynamics and interactions of turbulent structures and production in a flow-controlled turbulent boundary layer, and analyzing the applications of such viscous drag reduction. Wind tunnel experiments were performed on a zero pressure gradient turbulent boundary layer utilizing a wall mounted pulsed-DC DBD plasma actuator array to achieve positive skin friction drag reduction as well as net power savings. Hot wire measurements and diagnostics revealed a strong control of spanwise mean flow distortion and the intensity of measured turbulence kinetic energy demonstrating the effect of the flow actuation. Further analysis revealed a marked decrease in the wall-normal and streamwise vorticity components. These components are key in the cycle responsible for the production of the wall streak structures in the boundary layer and play an important role in the production and transportation of turbulent kinetic energy and as a result, viscous skin friction drag.