Dispersion of aircraft emissions due to wake vortices in stratified shear flows: A two-dimensional numerical study

The development of the wake vortex system behind an airplane (B-747) at cruising altitude (8-15 km) and the dispersion of the aircraft emissions due to this vortex system have been studied by means of a two-dimensional numerical model. Simulation experiments are presented which examine the influence of atmospheric stratification and vertical wind shear on the combined vortex-emission system. Although the development of the vortex wake system can be influenced by three-dimensional effects (e.g., Crow instabilities), the undisturbed process can be approximated as a two-dimensional phenomenon, which allows the study of details of the vortex structures at small scales (length L approximate to 1 m) and the dispersion of engine exhausts at larger scales (L approximate to 100 m). The results of simulation experiments show that the maximum lifetime of the wake vortices (120 s less than or equal to T-v less than or similar to 300 s) as well as the descending rate (1.2 m s(-1) less than or equal to w(v) less than or equal to 2.4 m s(-1)) and the dispersion of the emitted substances depend on the atmospheric stratification as well as vertical wind shear, but buoyancy forces seem to dominate over shear forces. The overall dispersion of aircraft emissions due to the wake vortex system can be quantified by a vertical standard deviation for the entire process of about sigma(z) less than or equal to 70 m.