Vortical flow characteristics of a slender delta wing in ground effect

Abstract

This study examined the ground effect on the vortical flow structures over a 70-deg-swept slender delta wing qualitatively and quantitatively using dye flow visualization and Particle Image Velocimetry techniques. The observations with dye visualization and PIV methods were conducted in the plan-view, side-view, and end-view planes with the angles of attack of alpha = 25 and 35. The distance, h between the delta wing and the ground surface nondimensionalized with the chord, c of the delta wing, was considered as h/c = 0.1, 0.25 0.55 as well as the ground-free effect flow condition. Also, the experiments were performed at a normalized chordwise location of x/c = 0.8 over the end-view plane. The results demonstrate that magnitudes of leading-edge vortices pro-gressively diminish when the delta wing moves from the ground-free effect region towards the wing location, h/c = 0.1. Also, the rate of inboard flow from the side leading-edge towards the central axis of the wing gets higher by the influence of the ground over the suction surface of the wing. When the wing altitude is lowered towards the ground surface, the size of the leading-edge vortex core region enlarges for both angles of attack, alpha = 25, and 35. The efficiency of the wing aerodynamics is positively affected by its closeness to the ground due to the air cushion effect that occurs as a result of the pressure increase on the suction surface of the wing due to the stagnation of air in the space between the delta wing and ground.