Computational analysis of vortex wakes without near-field rollup characteristics

A computational study on the wake characteristics of span-optimized wings is discussed, where the effect of the wing spanload on the resulting wake rollup characteristics and structure is emphasized. Two wing configurations, each optimized for minimum induced drag at a fixed C_L and fixed bending-moment constraint, are studied; and their wake characteristics are compared against an elliptically loaded wing. Results from Navier-Stokes simulations across the near-field wake demonstrate a symmetric large-scale rotation of the entire wake structure, centered roughly at the quarter-span location, for the bending-optimized wings. This wake structure is contrasted with the classical tip vortex formation associated with the elliptic spanload, which occurs immediately in the wing near-field wake. The far-wake structure was also studied using a free-wake simulation approach. The results from this analysis indicate a gradual rollup of the entire wake far downstream for the bending-optimized wings. This absence of wake rollup in the near field is envisaged as a potential means to reduce vortex interactions with downstream surfaces of aircraft and prevent other adverse operational challenges associated with wingtip vortices.