Wing-Tip Vortices, Turbulence, and the Distribution of Emissions

The decay of wing-tip vortices under the in uence of turbulence in a stably strati ed atmosphere is discussed by means of large-eddy simulations. The vortices originate from a B-747 aircraft in cruise. Atmospheric turbulence and turbulence originating from the boundary layer around the aircraft are distinguished. The former is weak and anisotropic with eddy sizes in the order of the wing span, whereas the latter is wrapped around the vortices with the maximum intensity at the core diameter. During their descent, the parallel vortex tubes approach each other because strati cation and turbulence detrain mass into the ambient air. The atmospheric eddies deform the trailing vortices such that their spacing varies. This, in turn, yields different mutually induced velocities that amplify the deformation quickly according to Crow’s instability theorem. The bent vortex tubes link after about 1.5 min and form rings. The continuous trail of turbine exhaust is reorganized in a row of single puffs. Without any atmospheric turbulence the vortices approach each other but remain parallel. They start to dissolve after 2 min when they touch. This dissolution is triggered by the small-scale boundary-layer turbulence. The exhaust trail remains aligned along the ight track. I.