Trailing Vortex Rollup from a Wing Equipped with a Gurney Flap

Abstract

Introduction T RAILING vortices and the hazard they pose to following aircraft have been studied by many researchers since the 1970s.1 Although many attempts to minimize the wake vortex problem have been examined, the strong adverse effect on the performance of the wake generating airplane has precluded their use. The present work explores the use of a Gurney flap as a wake vortex alleviation device. A Gurney flap is a narrow rectangular plate that is installed at the trailing edge of a wing on its pressure side as shown in Fig. 1. The typical height of the Gurney flap is 1–5% of the wing chord. The flap was first introduced by Gurney in the 1970s to improve the cornering speeds of racecars. Liebeck2 studied the effect of the Gurney flap on the performance of a Newman airfoil and found that a flap with a height of 0.01c increased the lift and decreased the drag. Storms and Jang examined the effect of a Gurney flap and/or vortex generator on the performance of a rectangular wing.3 They reported an augmentation of lift with Gurney flaps; this augmentation increased with increasing flap height. Ashby examined the effects of the height and location of Gurney flaps on the lift, drag, and pitching moment characteristics of a two-element rectangular wing.4 The effects of Gurney flaps on airfoils, wings, and a reflection plane model were investigated by Myose et al.5 The Gurney flap improved CL ,max of the flap-equipped configurations compared to the baseline configurations.5 Jeffrey et al. studied a single-element wing fitted with a Gurney flap.6 The Gurney flap increased the lift at a given prestall angle of attack but increased drag at most values of CL . Despite a reduction in the stall angle of attack, the Gurney flaps increased CL ,max. Buchholtz and Tso studied the effects of leadingedge fences and Gurney flaps, both separately and in combination, on the performance of a 60-deg delta wing.7 The Gurney flap was observed to increase the lift. Li and Wang tested delta wings with and without riblets and Gurney flaps.8 They found that all Gurney flaps increased CL and the larger flaps were more effective. Gai and Palfrey conducted experiments on a wing equipped with 0.05c Gurney flaps; both solid and serrated Gurney flaps were examined.9 Both flaps increased the lift, but reduced the stall angle of attack. The (L/D)max for both configurations was about 7% less than for the baseline configuration. Lin et al.10 tested a rectangular wing with a Gurney flap. The effects of the angle between the wing’s pressure surface and the flap and the distance between the flap and the wing trailing edge were studied. They found that all Gurney flap configu-