Description: The proposed research effort explores the use of a nanosecond pulse driven offset semiconducting surface dielectric barrier discharge (SSDBD) device for the control of high speed, near surface air flows and the reduction of skin friction drag. With the nanosecond discharge, very high field strengths are applied and then the field is turned off before glow-to-filamentary transition occurs. The semiconducting surface array suppresses the backward breakdown that has previously been shown to produce a cancelling backward jet leading to very little thrust for conventional nanosecond driven devices. The embedded semiconductors achieve this by conducting the backward current through the surface and thus eliminating the backward breakdown. This allows all the momentum produced in the forward direction to be delivered to the surrounding boundary layer flow field. Conventional sinusoidal driven Surface DBD's are capable of generating surface jets with velocities up to ~10 meter per second, limited by glow-to-filamentary transition of the discharge. The proposed SBIR work will explore the possibility of increasing the surface jet velocity by more than a factor of five. In addition, the SSDBD can be driven at a very high repetition rate, producing high repetition sequential surface jets and total thrust that are expected to be orders of magnitude higher than possible with conventional sinusoidal DBD configurations. These surface jets are expected to provide new methods for the control of boundary layer interactions including separation, transition to turbulence, and drag through the introduction of time varying momentum at selected locations close to the surface.

Benefits: Potential flow control applications of interest to NASA, based on the delay or early initiation of laminar-to-turbulent transition by manipulating near wall instability mechanisms, includes steering moments, reduced viscous drag, enhanced mixing, and reduced heat transfer. The SSDBD device may also be useful for reducing viscous drag, heat transfer, and fatigue caused by cyclic loading due to airframe vibration. These specific applications are achievable by controlling shock-induced boundary layer separation encountered in compression ramp geometries.

The potential flow control capabilities of the nanosecond pulse driven, offset semiconducting surface dielectric barrier discharge (SSDBD) device are not limited to NASA flight vehicles. In particular, the manipulation and control of subsonic instabilities such as stationary crossflow vortices by discrete roughness elements in the form of plasma bumps could potentially delay laminar-to-turbulent transition, greatly reducing viscous drag. In addition, the use of this device should be able to control boundary layer separation which would reduce viscous drag, and fatigue caused by cyclic loading due to airframe vibration.