A complete look at the near-field development and subsequent role-up of a wingtip vortex from a NACA 0015 wing section is investigated. Two separate but equally important surveys of the vortex structure in the region adjacent to the wingtip and approximately one chord length downstream of the trailing edge are performed. The two surveys provide qualitative flow-visualization an quantitative velocity measurement data. The near-field development and subsequent role-up of the vortex structures is strongly influenced by the angle-of-attack and the end-cap treatment of the wing section. The velocity field near the wingtip of the NACA 0015 wing section was measured with a triple-sensor hot wire probe and compared to flow visualization images produced with titanium tetrachloride smoke injection and laser illumination. The flat end-cap results indicate the formation of multiple, relatively strong vortex structures as opposed to the formation of a single vortex produced with the round end-cap. The multiple vortices generated by the flat end-cap are seen to rotate around a common ce te in a helical pattern until they eventually merge into a single vortex. Compared to a non-dimensional loading parameter, the results of the velocity and flow visualization data shows a "jetlike" axial velocity profile for loading parameter values on the order of 0.1 and a "wakelike" profile for much lower loading parameter values.Anderson, Elgin A. and Wright, Christopher T.Langley Research CenterWING TIPS; VORTICES; SUBSONIC WIND TUNNELS; AERODYNAMIC CONFIGURATIONS; AERODYNAMIC CHARACTERISTICS; FLOW VISUALIZATION; ANGLE OF ATTACK; TRAILING EDGES; VELOCITY DISTRIBUTION

"An experimental study of the effect of ground proximity on wingtip vortices has been conducted for swept and tapered wing with NACA 0015 profile over a stationary flat surface in a subsonic wind tunnel. The spatial growth and development of the vortex system generated by the swept and tapered wing with and without winglet arrangement have also been studied. It has been noted that with the reduction in ground proximity, the vortex system moved outward along the spanwise direction by 20% of the wingspan, and it moved closer to the ground. In close ground proximity, vortex rebound occurred due to a lack of space for movement of the vortex. For ground proximity of 15% root chord, a co-rotating ground vortex has been observed, and at 5% of root chord, a counter-rotating secondary vortex has been noticed. The interaction of these different vortices has led to the change of the shape of the entire vortex system.The calculation of lift-induced drag has also been computed using vw-crossflow measurements in the near wake region. It has been observed that the lift-induced drag decreases with reducing ground distance. At ground proximity of 5% root chord distance, a 20% decrease in lift-induced drag is seen compared to lift-induced drag outside ground effect. Also, with the addition of a 90° winglet, an average decrease of 5% lift-induced drag is seen when compared to the wing without a winglet. The lift coefficient has been estimated using the circulation of the vortex system both inside and outside ground effect. It has been noted that there is a 53% increase in the coefficient of lift at 5% ground proximity compared to the coefficient of lift outside ground effect. It has been found that the trend of coefficient of lift versus the ground distance matches the trend of other wing planforms and increases exponentially as the ground proximity decreases below 10% root chord. It has been concluded that the swept wing with a 90° winglet arrangement has been found to outperform all other arrangements"--