Combined effect of surface coating and angle of attack on the aerodynamic performance of NACA 0012, 4412, and 6412 airfoils

In this study, coated surfaces were used to investigate the effects of varying surface roughness on the aerodynamic performance of uncambered (NACA 0012) and cambered (NACA 4412 and 6412) airfoils in wind tunnel experiments. Surface roughness with different grit sizes, identified by the Coated Adhesive Manufacturing Index (CAMI) – R-120, R-180, R-240, R-320, R-600, and R-1000, was used to examine their impact on lift and drag forces. The experiments were performed at angles of attack (AOA) of 0°, 2°, 4°, 6°, and 10°, with freestream velocities between 3 and 15 m/s, and airfoils’ aspect ratio of 1.89. Results revealed that the coefficient of lift ( Cl ) and the coefficient of drag ( Cd ) correlated with AOA, showing different trends as velocity increased, with optimal performance observed at AOAs between 4° and 6°. The effects of surface roughness were measured using normalized ratios of lift and drag coefficients of rough-surfaced airfoils to those of smooth-surfaced airfoils, denoted as Cl ratio and Cd ratio . Coarser surfaces of cambered airfoils improved lift and reduced drag, particularly at lower velocities and smaller AOAs, with NACA 6412, reaching 3.0. NACA 0012 showed better lift at 0° AOA with surface roughness, while NACA 6412 had the highest lift-to-drag ratios ( L/D ) due to increased camber. In general, smoother surfaces performed better for cambered airfoils, producing higher L/D , while coarser roughness benefited NACA 0012. The study concludes that carefully managing surface roughness can significantly influence airflow behavior and provides insights into the design of aerodynamically efficient airfoils. • Aerodynamic performance of NACA 0012, 4412 and 6412 at various surface conditions and angle of attacks (AOA) were carried out. • The aerodynamic performance of the airfoils showed a strong correlation with its surface conditions and AOA. • Optimal aerodynamic efficiency for both smooth and rough surface was achieved at AOAs of 4° and 6°. • The introduction of rough elements introduced on the NACA 0012 improved its lift coefficient at 0° AOA. • The more cambered, NACA 6412 was sensitive to surface roughness, especially at high AOAs.