Numerical investigation of the aerodynamics of an airfoil in mutational ground effect

The takeoff and landing processes of a NACA 4412 airfoil on a platform at a constant speed are simulated. The angle of climb in takeoff and the glide angle in landing are all assumed zero. The takeoff process of the NACA 4412 airfoil on a platform can be divided into four phases. In phase I, the airfoil gradually approaches to the side of the platform, and the lift keeps the stable value in static ground effect. In phase II, the leading half part of the airfoil leaves the platform, the static ground effect gradually disappears, and the downwash flow decreases the effective angle of attack (AOA); therefore, the lift sharply drops. In phase III, the airfoil completely leaves the platform, the static ground effect completely disappears, and the downwash flowweakens, but the latter is the main controlling factor; thus, the lift increases. In phase IV, the lift and airflow around the airfoil all gradually tend to the situations in the unbounded flowfield. The phase characteristics of the lift curves during takeoff and landing processes do not change with the increasing AOA, and the fluctuating amplitude of the unsteady lifts decreases with the increasing ground height.