PhD Candidate Christopher L. Kelley - "Airfoil Leading and Trailing Edge Separation Control Using SDBD Plasma Actuators"
|Start:||11/20/2013 at 10:00AM|
|End:||11/20/2013 at 12:00PM|
Wind tunnel experiments were conducted to understand boundary layer separation control onairfoils. The objective of this research was to better implement flow control strategies with singledielectric barrier discharge (SDBD) plasma actuator designs for airfoils that exhibit both leadingand trailing edge stall characteristics at realistic flight speeds and Reynolds numbers. The NASAenergy efficient transport (EET) airfoil was a platform to study the effect of plasma actuators onleading edge stall and boundary layer separation in a strong adverse pressure gradient, while theV-22 Osprey airfoil was used to study trailing edge stall with separation in a weaker adverse pressuregradient.The EET airfoil was designed to have a spanwise plasma actuator on removable leading edges madefrom two different dielectric materials: Kapton and Macor. Two different plasma waveforms werealso tested with the same electrodes, AC (alternating current) and nanosecond pulse (NP) driven.Aerodynamic force and moment measurements showed that both plasma actuators were effectiveat increasing the stall angle of attack and maximum lift for the range of Mach numbers tested,0.1–0.4, and Reynolds numbers of 560,000–2,240,000. This indicated that the shear layer instabilitywas highly receptive to both disturbances: either the body force from AC plasma actuator, or thenondirectional thermal disturbance of the NP plasma actuator. The shear layer instability alsoprovided for an opportunity to quantify the effect of unsteady, or duty cycle, operation. The liftto drag ratio of the EET airfoil was improved the most by operating the AC plasma actuator at areduced frequency of unity and the NP plasma actuator at 2 or higher.The second part of the experiment examined the efficacy of plasma actuators on a V-22 airfoil fortrailing edge separation control in the presence of new factors such as moving separation location,crossflow, turbulent boundary layers, and weaker pressure gradients at the line of vanishing shear.Initial consideration of moving separation location with angle of attack motivates the use of plasmastreamwise vortex generators (PSVGs) which take up a larger percent of the chord dimension andproduce streamwise vorticity from both crossflow momentum addition and by reorienting spanwisevorticity from the boundary layer. The PSVGs were compared to traditional passive vortex generators(VGs). These devices were installed on the wing section by which the angle of attack could beused to vary the streamwise pressure gradient. The experiment was performed for freestream Machnumbers 0.1–0.2 and a Reynolds number range of 790,000–1,590,000. Three-dimensional velocitycomponents were measured using a 5-hole Pitot probe in the boundary layer. These measurementswere used to quantify the production of streamwise vorticity and the magnitude of the reorientationterm from the vorticity transport equation. Reductions in drag were well correlated to streamwisevorticity production. For the PSVG, vorticity production was proportional to the residence timescaleof freestream momentum and operating voltage. These results indicate that the PSVGs could easilyoutperform the passive VGs and provide a suitable alternative for flow control. Finally, a designequation was proposed to create a PSVG equivalent to a VG including design parameters such asMach number, angle of attack, operating voltage, and electrode length.