Influence of different flap settings on the wake-vortex structure of a rectangular wing with flaps and means of alleviation with wing fins

This paper presents the results of an experimental investigation of the wake-vortex structure behind a flapped rectangular wing. The wind-tunnel test is part of a project funded by the German Research Association (DFG) to investigate the flow structure in the wake of wings with different flap extensions. The purpose of this investigation is to study the main features of lift generated vortices in order to find ways to alleviate hazardous wake vortex encounters for following airplanes during start and approach such that an increase in airport capacity can be achieved. First, the wake structure at different flap settings is investigated by measuring the velocity field at different positions in the near field behind the wing. The measured data are evaluated in terms of vortex parameters such as core radius, maximum tangential velocities, circulation distributions, turbulence levels and maximum induced rolling moments on a following aircraft. Then additionally, for one flap setting, means of alleviation are examined with a wing fin mounted at different positions on the wing. Alleviation is judged by the decrease of the maximum induced rolling moment. A significant reduction is achieved for a wing fin placed near the outboard edge of the flap.