Lift-generated vortex wakes of subsonic transport aircraft

The flow fields of vortices, whether buoyancy-driven or lift-generated, are fascinating fluid-dynamic phenomena which often possess intense swirl velocities and complex time-dependent behavior. As part of the on-going study of vortex behavior, this paper presents a historical overview of research conducted on the structure and modification of the vortices generated by the lifting surfaces of subsonic transport aircraft. Although primarily presented from an experimental point of view, the derivation and use of relatively compact theoretical formulations and concepts are included. Experience with lift-generated wakes has shown that they are so complex that progress requires application of a combined theoretical and experimental research program, because either alone often leads to incorrect conclusions. The primary purpose of the research to be described is to find a way to reduce the hazard potential of lift-generated vortices shed by subsonic transport aircraft in the vicinity of airports during landing and takeoff operations. The information presented points out that the characteristics of lift-generated vortices are related to the aerodynamic shapes that produce them and that various arrangements of surfaces can be used to produce quite different vortex structures. It is concluded that a satisfactory aerodynamic solution to the wake-vortex problem at airports has not yet been found, but a reduction in the impact of the wake-vortex hazard on airport capacity may soon become available through wake-vortex avoidance concepts currently under study.