Towards laminar flow control on swept wings with AC-DBD plasma actuators as active roughness

In the present work, laminar flow control, following the distributed roughness elements (DRE) - upstream flow deformation (UFD) strategy, was attempted on a 45° swept wing at Re = 2:17·10⁶undergoing cross-flow (CF) instability transition. Active roughness-like AC-DBD plasma actuators were used for this purpose. Specialized patterned actuators have been designed, manufactured and tested to this goal. The effectiveness in forcing monochromatic stationary modes was assessed by means of infrared thermography. Finally, quantitative measurements of the transitional boundary layer were performed with high-speed PIV. This advanced flow diagnostics tool allows the investigation of the effects on the boundary layer of the unsteady forcing, inherent to the effect of the used actuators. It is found that, despite the actuators were operated at a frequency considerably larger than the frequency band of the (primary travelling) CF instability, the latter resulted massively amplified by the actuation. The causes of this phenomen are here only conjectured and require future dedicated investigation. The eventual beneficial effects of the DRE/UFD flow control technique are likely overwhelmed by the nocent amplification of travelling modes. The technological possibility of very high frequency forcing therefore can limit the usage of AC-DBD actuators for DRE/UFD laminar flow control in high Reynolds numbers flows.