Experimental Investigation On Aerodynamics Characteristics And Tip Vortices Of A Wing In Ground Effect

The tip vortices and aerodynamics of a NACA0012 wing in the vicinity of the ground were studied in a wind tunnel. The wing tip vortex structures and lift/drag forces were measured by a seven-hole probe and a force balance respectively. The evolution of the flow structure and aerodynamics with ground height were analyzed and investigated. The vorticity of tip vortices was found to reduce with the decreasing of the ground height, and the position of vortex-core moves gradually to the outboard of the wing tip, therefore, the down-wash flow induced by the tip vortices was weakened and increased the effective angle of attack. Moreover, the life/drag forces increased with the decreasing of ground clearance, as the induced drag decreasing. However, vortex breakdown occurred as the wing lowered to the ground. From the experimental results of aerodynamics, the maximum lift-to-drag ratio was observed when the angle of attack was 2.5°and the ground clearance was 0.2. Experimental results also showed that increasing of static pressure gradient in the vortex core could accelerate the dissipation rate of wing tip vortex downstream.In addition, the ground effect of a wing in proximity to a free water surface was studied in the wind-wave tunnel by measuring the lift/drag and the tip vortex structures. The experimental results were compared with that of the wing in fixed ground effect. It was found that the lift and drag wing near free surface are larger than that of the wing near fixed ground. Velocity distribution of the wing near free surface is more complicated and the vorticity of wing tip vortex was stronger compared with that of a wing near a fixed ground.The experimental data reflect the impact of tip vortex structures with the aerodynamic characteristics of WIG. The experimental results of present study provide an important reference for the further investigation of the WIG in the future.