Multifactorial Effects of Operating Conditions of Dielectric-Barrier-Discharge Plasma Actuator on Laminar-Separated-Flow Control

Abstract

A substantial number of large-eddy simulations are conducted on separated flow controlled by a dielectric barrier discharge plasma actuator at a Reynolds number of 63,000. In the present paper, the separated flow over a NACA 0015 airfoil at an angle of attack of 12 deg, which is just poststall, is used as the base flow for separation control. The effects of the location and operating conditions of the plasma actuator on the separation control are investigated by a parametric study. The control effect is evaluated based on the improvement of not only the lift coefficient but also the drag coefficient over an airfoil. The most effective location of the plasma actuator for both lift and drag improvement is precisely confirmed to be upstream of the natural separation point. Even a low burst ratio is found to be sufficient to obtain the same improvements as the cases with a high burst ratio. The effective nondimensional burst frequency F is observed at 4 ≤ F ≤ 6 for the improvement in the lift coefficient and at 6 ≤ F ≤ 20 for that in the drag coefficient.The lift/drag ratio shows a clear peak at 6 ≤ F ≤ 10. To clarify the mechanism of the laminar-separation control, the effect of a turbulent transition is investigated. There is a clear relationship between the separation control effect and the turbulent transition at the shear layer. An earlier and smoother transition case shows greater improvements in the lift and drag coefficients. Flow analyses show that the cases with early and smooth turbulent transition can attach the separated flow further upstream, resulting in a higher suction peak of the pressure coefficient. In addition, another mechanism of the separation control is observed in which the lift coefficient is improved, not by the reattachment through the turbulent transition but by the large-scale vortex shedding induced by the actuation. It is possible to separate these two dominant mechanisms based on the effect of the turbulent transition on the separation control. Nomenclature a = speed of sound BR = burst ratio C D = drag coefficientlength scale D c = ratio between electrostatic body force added by plasma actuator and dynamic pressure D c;effe = effective D c value E i = electric field vector induced by plasma actuator e = total energy per unit volume F base = nondimensional base frequency for sine wave of input voltage; f base c∕u ∞ F = nondimensional frequency of burst wave; f c∕u ∞ f = frequency f base = base frequency for sine wave of input voltage f = frequency of burst wave M ∞ = freestream Mach number Pr = Prandtl number p = pressure Q c = electric charge q i = heat flux vector Re = Reynolds number St = Strouhal number S Suzen = body force vector determined from Suzen model S i = body force vector; Q c E i T = burst wave period T base = period of sine wave T off = period when sine wave switch is off during burst wave period T on = period when sine wave switch is on during burst wave period t = time u = velocity in chord direction . Member AIAA. Article in Advance / 1 AIAA JOURNAL Downloaded by U...

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