PHYSICAL FEATURES AND VORTEX WANDERING OF WINGTIP VORTICES FOR THREE DIFFERENT TIP CONFIGURATIONS

For different tip configurations, the wingtip vortices have distinct vortex structures and vortex wandering behavior, which indicates the slow side-to-side movement of the wing-tip vortex core behind the wing and is one result of a vortex instability. In this paper, the vortex structures and vortex wandering behaviors of wingtip vortices for three typical tip configurations, namely, square-cut, raked winglet, and blended winglet wingtips, are experimentally investigated by using the particle image velocimetry (PIV) technique. The results based on three different Reynolds number clearly show that winglets can effectively reduce the strength of wingtip vortices. In addition, the wingtip vortices for different wingtip configurations have distinct structures, tangential velocity profiles, and trajectory characteristics. By tracking the instantaneous center of the vortex core, it is found that the wandering amplitude of wingtip vortices is amplified with downstream position for the three tip configurations. Moreover, the wandering amplitude for raked and blended winglet wingtips is much smaller than that for square-cut wingtip, and the wingtip vortex for blended winglet configuration has the smallest wandering amplitude than those for the other two configurations. Accordingly, it is concluded that winglets can not only reduce the circulation of tip vortices, but also change the tip-vortex structures to weaken vortex wandering amplitude.