Dynamic stall control over an airfoil using plasma co-flow jet

To enhance the dynamic stall performance of airfoils, this study investigates the National Advisory Committee for Aeronautics 0025 airfoil and a modified Plasma Co-Flow Jet (PCFJ) airfoil through pressure distribution measurements and Particle Image Velocimetry experiments conducted in both still air and wind tunnel environments. Additionally, numerical simulations are conducted using the unsteady Reynolds-Averaged Navier–Stokes equations with the transitional Shear-Stress Transport turbulence model. At a Reynolds number of 6.7×104 and a mean angle of attack of 15°, the flow control characteristics of the PCFJ airfoil during dynamic stall are analyzed under various duty-cycle reduced frequencies (f+=0.4−40.0). In still air, experimental results show that the induced flow field on the airfoil's upper surface evolves from large-scale starting vortex structures to small-scale vortices, ultimately into a continuous shear layer as the duty-cycle frequency increases. Under free-stream conditions, a pitch amplitude of 5° is selected as a representative case of mild stall. In this regime, steady-on and duty-cycle actuation effectively suppress the formation of large-scale separated vortices. Duty-cycle actuation, in particular, demonstrates superior performance by increasing the maximum lift coefficient by 38.7%, reducing the minimum drag coefficient and peak nose-down pitching moment coefficient by 50.4% and 63.3%, respectively, and significantly shrinking the hysteresis loop area. When the pitch amplitude increases to 15°, representing a deep-stall condition, flow separation and hysteresis effects are intensified considerably. In this case, steady-on actuation proves more effective, increasing the maximum lift coefficient by 32.6%, and reducing the maximum drag and peak nose-down moment coefficients by 43.8% and 53.5%, respectively. Furthermore, the structure of dynamic stall vortices and the resulting aerodynamic behavior are susceptible to the duty-cycle reduced frequency. At f+=0.4, plasma actuation suppresses the formation and development of large-scale separated vortices on the airfoil's upper surface. At f+=4.0, the flow exhibits a sequence of small-scale, quasi-ordered vortex structures with a notable lift-enhancing effect, increasing the maximum lift coefficient by 24.7%. At f+=40.0, the flow appears as a stable shear layer, resulting in the most significant reduction in the nose-down moment, with the peak moment coefficient reduced by 47.4%.