Large-eddy simulation of Reynolds number effects on pre-stall airfoil-flow control using vortex-generator type plasma actuators

Large-eddy simulations on pre-stall airfoil-flow control using vortex- generator type plasma actuators (VG-PA) have been conducted. The control performance was evaluated under different Reynolds number conditions: Re = 5,000, 10,000, and 63,000 at 4 deg angle of attack, and Re = 260,000 at 8 deg. The effects of VG-PAs were compared with those of spanwise plasma actuators. Additionally, two driving methods, continuous and burst actuations were examined for the VG-PA. Simulation results demonstrate that VG-PAs with burst-mode consistently achieved the highest lift-to-drag ratio over all Reynolds numbers. However, the control mechanisms exhibited distinct Reynolds-number dependence. At higher Reynolds numbers (Re=63,000-260,000), burst actuation resulted in earlier turbulent transition, and suppressed laminar separation bubble formation, leading to pressure drag reduction. This pressure drag reduction mainly contributes to the high lift-to-drag ratio at higher Reynolds number conditions. At lower Reynolds numbers (Re=5,000-10,000), the VG-PA control slightly suppressed laminar separation occurring beyond mid-chord, resulting in lift increase. This lift enhancement mainly contributes to high lift-to-drag ratio at lower Reynolds number conditions. Regarding skin friction, actuation increased friction drag in all cases. The increase in friction drag is more pronounced for VG-PA control cases because of the generation of turbulent vortices.