Large-eddy simulations of a coherent counter-rotating vortex pair in different environments are performed. The environmental background is characterized by varying turbulence intensities and stable temperature stratifications. Turbulent exchange processes between the vortices, the vortex oval, and the environment, as well as the material redistribution processes along the vortex tubes are investigated employing passive tracers that are superimposed to the initial vortex flow field. It is revealed that the vortex bursting phenomenon, known from photos of aircraft contrails or smoke visualization, is caused by collisions of secondary vortical structures traveling along the vortex tube which expel material from the vortex but do not result in a sudden decay of circulation or an abrupt change of vortex core structure. In neutrally stratified and weakly turbulent conditions, vortex reconnection triggers traveling helical vorticity structures which is followed by their collision. A long-lived vortex ring links once again establishing stable double rings. Key phenomena observed in the simulations are supported by photographs of contrails. The vertical and lateral extents of the detrained passive tracer strongly depend on environmental conditions where the sensitivity of detrainment rates on initial tracer distributions appears to be low.

On the one hand, it is known from visual observations, Lidar measurements, and numerical simulations that aircraft wake vortices may live significantly longer than anticipated by todays standard regulations of air traffic control. On the other hand, the initially counterrotating, parallel vortex pair deforms quickly, which reduces the impact time of adverse forces and moments on encountering aircraft. Therefore, large-eddy simulations of wake vortex evolution in different meteorological conditions are conducted in order to analyse the physics of vortex deformation. A new post-processing algorithm has been developed that at first determines the three-dimensional path of the vortex core line and then computes piecewise curvature radii as a measure of vortex deformation. It is found that larger turbulence levels and neutral to weakly stable temperature stratification particularly support vortex ring formation. The vortex ring regime is characterized by a reduced descent rate and by a surprising variability of its core radius. It is shown that the varying core size directly affects the evolution of radii-averaged circulation. Comparisons with field experiments indicate good agreement with the considerable life time of the vortex rings and topology.

Large eddy simulations (LES) 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.

Large-scale distortion of aircraft wake vortices appears to play a crucial role for aircraft safety during approach and landing. Vortex distortion is investigated based on large eddy simulations of wake vortex evolution in a turbulent atmosphere. A vortex identification method is developed that can be adapted to the vortex scales of interest. Based on the identified vortex center tracks, a statistics of vortex curvature radii is established. This statistics constitutes the basis for understanding, modeling, and exploiting mitigation effects of vortex distortion on wake vortex encounters.