Winglet Dihedral Effect on Flow Behavior and Aerodynamic Performance of NACA0012 Wings

Abstract

This study investigates the effects of Reynolds number, angle of attack, and winglet dihedral (δ) on the smoke-streak flow patterns, surface oil-flow configurations, and aerodynamic performance of the wingleted wings. The airfoil is NACA 0012 and the winglet dihedral varies from −30° to 135°. The smoke-wire technique was utilized to visualize the three-dimensional flow structures. Furthermore, the effect of δ on the wingtip surface vortex was examined using the surface oil-flow scheme. The wingtip surface vortex was observed on a baseline wing using the smoke-streak flow and surface-oil flow visualization schemes. Moreover, the length of wingtip surface vortex (Lb) decreases with increasing δ for δ > 15° where Lb denotes the major axis of wingtip surface vortex. The maximum Lb/C of 1.2 occurs at δ = 15° which is about 42% higher than that of a baseline wing, where C represents the wing chord length. The high flow momentum expands the wingtip surface vortex toward the winglet when δ < 15°. However, the minimum Lb/C of 0.55 occurs at δ = 90° which is about 34% lower than that of a baseline wing because the wingtip surface vortex is squeezed intensely at high δ. The aerodynamic performance was measured using a force-moment balance. The experimental data indicates that the lift-drag ratio at stalling (CL/CD)stall and maximum lift-drag ratio (CL/CD)max occurs at δ = 90°.