Large-eddy simulation of aircraft wake vortex deformation and topology

Abstract: 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 counter-rotating, 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 evolu-tion 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 cir-culation. Comparisons with field experiments indicate good agreement with the considerable life time of the vortex rings and topology.