Boundary Layer Flow Acceleration by Paraelectric and Peristaltic EHD Effects of Aerodynamic Plasma Actuators

Plasma actuators based on the OAUGDP TM (One Atmosphere Uniform Glow Discharge Plasma) promise to be a convenient method to modify aerodynamic boundary layers. The development of the OAUGD Plasma has made it possible to locate enough plasma actuators on airfoils and the wings and fuselage of aircraft to have significant effects on flow control and re-attachment at relatively low power cost. In this study OAUGD Plasma actuators have been used to effect flow re-attachment and to manipulate aerodynamic flows, possibly leading to improved methods of flight control. The OAUGDPTM actuators have been tested in the 7 x 11 Inch Low Speed Wind Tunnel at the NASA Langley Research Center during several experimental campaigns that began in the mid 1990’s. The 7 x 11 Inch Low Speed Wind Tunnel is instrumented to conduct drag measurements, smoke flow visualization tests, Pitot tube velocity profile measurements and airfoil flow re-attachment visualization studies.

This thesis is concerned with two EHD (electrohydrodynamic) flow control methods that utilize only RF displacement currents to produce the body forces that accelerate the plasma; paraelectric and peristaltic (traveling wave) flow acceleration. Paraelectric flow acceleration is achieved when the applied electric field acts on the net charge density of the plasma, to provide a body force capable of accelerating the neutral gas to velocities as high as 10 m/sec. During the acceleration process, the plasma moves paraelectrically towards increasing electric field gradients, and drags the neutral gas along with it as the result of frequent ion-neutral Lorentzian collisions. Peristaltic flow acceleration results from a traveling electrostatic wave, analogous to the apparent motion of light in a phased array of bulbs on a theatre marquee. To produce a traveling electrostatic wave, adjacent plasma actuators are energized at progressively larger phase angles. The resulting horizontal electric field produces a body force that accelerates the plasma.

A OAUGDPTM panel or a plasma actuator intended for aerodynamic flow acceleration consists of linear strip electrodes adhering to either side of a dielectric panel. The actuators are energized using RF power at voltages between 0 and 10 kV, and frequencies between 0.5 kHz and 8 kHz. A major contribution described in this thesis was the development of flexible and ceramic panels, the polyphase signal generator based on LabVIEW, and accessories for the polyphase power supply. During development of the plasma actuators, many electrode geometries were tested to achieve the best operating conditions i.e. highest flow velocity. This thesis presents experimental results from several plasma actuator configurations, and performance data from both paraelectric and peristaltic flow acceleration.