Numerical simulation of the flowfield of an 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. In this paper, the landing process of a NACA4412 airfoil is simulated numerically to investigate the influence of dynamic ground effect. Several sinking rates are imposed on the airfoil. Analyses of the simulation results show that the dynamic ground effect 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 ride height region, the lift in the dynamic ground effect does not change with decrease in ride height and is equal to the lift in the static ground effect with the same angle of attack. The effect of the 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 ride height region, the lift in the dynamic ground effect increases with decreasing ride height and is almost equal to the lift in static ground effect with the same angle of attack. Both the static ground effect and the incidence effect due to sinking govern the flow field. In the small ride height region, the lift in the dynamic ground effect increases rapidly with decreasing ride height and is significantly larger than that in the static ground effect with the same angle of attack. Furthermore in this region, in addition to the static ground effect and the incidence effect due to sinking, the compression work effect becomes very important. At relatively small ride height, the air below the airfoil lower surface does not have sufficient space to escape due to the presence of the ground as the airfoil moves downwards towards the ground. Therefore this air gets compressed and the static pressure increases which enhances the lift. This is the so-called compression work effect.