Active Reduction of Skin Friction Drag

Aircraft range is limited, in part, by skin friction drag. Recent advances in control technology with small actuators such as piezoelectric materials and micro-electromechanical systems (MEMS) may make active boundary layer control for drag reduction practical. The unique characteristics of piezoelectric materials and MEMS are small size, fast response, and low energy consumption. Additionally, the controls can be integrated with modern electronics and readily produced in large quantities. In this proposal two control strategies will be pursued. First, transition in the boundary layer will be delayed as much as possible using wave cancellation techniques. Second, when transition becomes inevitable, large eddies that cause most of the drag in a turbulent boundary layer will be attenuated through concerted efforts from several neighboring controls. The basic control unit for achieving active boundary layer control cosists of three elements: (1) flow condition sensors, (2) feed-forward control devices, and (3) an array of actuators. In the Phase I investigation, the primary focus will be on developing effective active actuator devices. Simple wind tunnel experiments will generate upstream disturbances on a flat plate and various flow control devices and their motions relative to the artificial upstream disturbance will be evaluated for potential drag reduction benefits.