Study of Transient and Unsteady Effects of Plasma Actuation in Transitional Flow over an SD7003 Airfoil

Abstract

The short term transient and long term periodic unsteady effects of pulsed plasma actuation are studied using an unsteady, compressible Navier-Stokes solver for the case of a partially separated transitional flow over an SD7003 airfoil at 4º angle of attack and at Re=40,000. Forcing magnitude and its effect on the flow field is examined. Distinctly different behavior is observed parameters are adjusted. The unsteady simulations show that the actuators have a quick transient response, reattaching the separated flow within 2 nondimensionalized units of time, but nearly independently of the forcing magnitude. Spikes in C l , C d , and C m are observed during reattachment, most likely due to vortex pairing at the trailing edge.

Numerical Investigation of Serpentine Plasma Actuators for Separation Control at Low Reynolds Number

“…The lift and drag for the cases of pulsed actuation also shows oscillatory behavior, but that behavior is consistent with the St=5 forcing frequency (Figure 20). Additionally, aside from a slight increase for the fullest serpentine geometry, the magnitude of the oscillations increases as the geometry compresses, possibly resulting from the more coherent vortical structures in the boundary layer passing over the trailing edge all at once (similar effects with spanwise vortical structures were seen previous work [10][11] ). These oscillations are also smaller than those of the uncontrolled or of the continuously actuated case.…”

“…Though the variation of the geometry shows some impact on the lift and drag, it seems that the largest driver is whether or not the plasma forcing is pulsed or not, thus indicating that the unsteady stability is the most important thing to reattaching the flow (Table 3). Pulsing the actuation seems to bring a drop in C L and C D , with corresponding rise in <C L /C D > of roughly 19%, similar to the effects of reattachment for the linear actuator geometries [10][11] . Only marginal changes appear with continuously run plasma actuation, where <C L /C D > increases only by 1.0%.…”

“…This flow also shows a quasi-periodic shedding of vortical structures starting within the laminar shear layer with a frequency around St=5, indicating that some sort of instability exists near that frequency. Previous 10,11 have taken advantage of this instability to remove the flow separation and those studies were able to produce an attached flow.…”

“…Plasma actuators can also be flush mounted such that they have no impact on the flow field when not in use. Furthermore, DBD plasma actuators have shown themselves to be effective for boundary layer control [4][5][6] and for flow reattachment at low Reynolds number [6][7][8][9][10][11] , especially when used in a pulsed manner, where unstable frequencies can be excited, causing the flow to transition and then reattach.…”

“…Plasma actuators with novel geometries, such as the serpentine geometry have shown themselves to be very useful in a number of numerical studies [11][12][13][14] as well as limited experimental work [15][16][17] . These actuators are able to introduce streamwise, as well as spanwise and surface normal vorticity to the flow, and promote increased mixing of the flow.…”