LARGE-EDDY SIMULATION OF TURBULENCE IN THE FREE ATMOSPHERE AND BEHINDAIRCRAFT

The method of large-eddy simulation has been used for a wide variety o f atmospheric flow problems. This paper gives an overview on recent ap plications of this method to turbulence in the free atmosphere under s tably stratified conditions. In particular, flows in the wake of aircr aft are studied in light of the potential impact of aircraft exhausts on the chemical and climatological state of the atmosphere. It is show n that different profiles of heat and moisture in the initial conditio ns of a jet representing engine exhaust gases may cause larger water s aturation and hence earlier contrail formation than assumed up to now. The instability of trailing vortices in the wake of an aircraft is si mulated up to the fully turbulent regime. The vertical diffusivity of aircraft exhaust is large in the vortex regime and much smaller than h orizontal diffusivities in the later diffusion regime. The three-dimen sional formation of a critical layer and breaking of gravity waves is simulated.