Mechanism of flow separation control using plasma actuation

The mechanism of flow separation control was investigated experimentally and computationally using pulse-modulated dielectric barrier discharge (DBD) plasma actuation on a stalled flat plate airfoil at a Reynolds number of 3000. Load measurements were complimented with two-dimensional phase-averaged particle image velocimetry performed in the flowfield above the airfoil. A parametric study was carried out where the pulse-modulation frequency, duty cycle, and peak plasma body-force were varied. The two-dimensional Navier-Stokes equations, with no turbulence modeling, were solved directly using a commercial flow solver and a simple but satisfactory heuristic DBD plasma body-force model was incorporated. The overall experimental trends were well predicted by the computations, where the frequencies that produced the largest increases in lift coefficient excited bluff-body shedding at a frequency corresponding approximately to its unforced sub-harmonic. At non-dimensional frequencies most effective for increasing lift (∼0.2 to 0.5), the leading-edge shear layer was severed by the perturbations and then merged with a downstream vortex. In a time-mean sense this mechanism forced relatively high momentum fluid towards the surface with typically two re-circulating structures present on the airfoil. Although the essential flow control mechanism was captured by the computation, the idealized 2D approach was identified as a weakness due to the shedding instability not being present in the baseline experiments and the inability to account for three-dimensional structures in the shear layer.