Numerical study of the aerodynamics of a NACA 4412 airfoil in dynamic ground effect

The distance between an airplane and the ground keeps constantly changing during take-off and landing. Thus, the aerodynamics is influenced by the dynamic ground effect (DGE). In this paper, the landing process of a NACA 4412 airfoil is simulated numerically to investigate the influence of DGE. Several sink rates are imposed on the airfoil. Analyses of the results show that DGE can be divided into three regions based on the aerodynamics and flow physics which depend upon the ride height above the ground. In the large height region, the lift in DGE does not change with decrease in height and is equal to the lift in static ground effect (SGE) with the same angle of attack. Ground effect is insignificant and the physics that governs the flow is due to the incidence effect induced by the sinking movement. In the medium height region, the lift in DGE increases with decreasing height and is almost equal to the lift in SGE with the same angle of attack. Both SGE and the incidence effect due to sinking govern the flow field. In the small height region, the lift in DGE increases rapidly with decreasing height and is significantly larger than that in SGE with the same angle of attack. Furthermore in this region, in addition to SGE and incidence effect, the compression work effect becomes very important. At relatively small height, the air below the airfoil does not have sufficient space to escape due to the blockage from the ground as the airfoil moves downwards towards the ground. Therefore this air gets compressed and its pressure increases which enhances the lift. This is the so-called compression work effect.