An experimental investigation into Stokes-layer formation with oscillating dielectric barrier discharges

An AC-DBD plasma actuator is experimentally characterized, proposing a novel flow-control concept for turbulent drag reduction, yet decisively enhancing its control authority compared to former strategies. Essentially, the exposed and encapsulated silver electrodes of 1 and 3 mm width (6 µm thickness), respectively, are adjacently placed on a 500 µm thick PET dielectric, featuring a spanwise wavelength λ_z=4 mm. The plasma-generation system comprises three HV transformers that switch the electric field on this multi-electrode array with a duty cycle of 50 %, hence exerting opposed body-force oscillations. High-speed PIV is used to acquire phase-resolved velocity data with two different magnifications (40 and 80 px mm^-1). Based on Re_τ = 250, an optimal oscillation period T⁺ = 125 (λ_z⁺ = 80) is applied (Gatti & Quadrio, JFM 2016). The momentum transfer to the near-wall fluid above the dielectric results in a Stokes-layer-like flow of a wall-normal range y⁺ < 10. Variations of the wall-parallel velocity magnitude are analyzed in terms of spanwise homogeneity across the electrodes and found to be significantly reduced. As such, the presented study demonstrates a valuable step towards an ideal Stokes layer, mimicking moving parts with plasma discharges.