Aerodynamics of an airfoil in dynamic ground effect during take-off

The dynamic takeoff process of NACA 4412 airfoil at a constant climbing acceleration from the ground is simulated by solving the Reynolds Averaged Navier-Stokes equations in conjunction with the SST k-ω turbulence model. The relative motion between the airfoil and the ground is dealt with by the dynamic layering mesh technology. The primary aim of this research is to clarify the difference between the dynamic ground effect (DGE) and the static ground effect (SGE) for the same ride height and angle of attack (AOA). The lift increment in DGE in contrast to the SGE with the same ride height and AOA is affected by the flow hysteresis effect and the vacuum effect. The flow hysteresis effect increases the effective AOA in the dynamic process and further increases the lift. The vacuum effect decreases the pressure on the lower surface of the airfoil near the ground, which further decreases the lift. With the increasing ride height, the flow hysteresis effect increases and the vacuum effect decreases, thus the lift increment in DGE first decreases and then increases.