Wake-vortex topology, circulation, and turbulent exchange processes

Large eddy simulations of aircraft wake vortex evolution in various turbulent and stably stratified atmospheric environments have been conducted with two different LES codes. Passive tracers are used to investigate exchange processes between the vortex cores, the vortex oval and its environment as well as redistribution processes along the vortex tubes. A post processing method is employed to identify the vortex center lines even in progressed states of vortex decay where the coherent vortex structure is getting lost. This method allows, for example, analyzing the circulation evolution of vortex rings, establishing statistics of vortex deformation, and revealing the mechanisms of the vortex bursting phenomenon. Vortex bursting is related to the collision of secondary vorticity structures propagating along the vortex lines. In neutrally and weakly stratified environments long-living vortex rings are observed where circulation decay proceeds in three phases. During the initial diffusion phase vortex decay may depend on integral turbulence length scales. On average, the detrainment of a passive tracer from the primary vortices is correlated with circulation decay.