Aircraft wake vortex decay in ground proximity - Physical mechanisms and Artificial Enhancement

Aircraft wake vortex evolution in ground proximity is investigated numerically with large eddy simulations (LES). The simulations are performed with different modifications of the ground surface in order to trigger rapid vortex decay or to simulate the landing of an aircraft. The impact of environmental turbulence in terms of turbulent winds is taken into account, where wall-resolved and wall-modeled LES are performed for low and high Reynolds number cases, respectively. In order to understand wake vortex decay mechanisms in ground proximity the interaction of primary and secondary vortices is thoroughly investigated. The results show that vortex decay is initiated and accelerated with obstacles at the ground. In order to optimize obstacle shape and size we show that we can achieve a similar effect with relatively small plates as with large block-shaped barriers. Concerning large Reynolds numbers we show that turbulence effects triggered by the ground can not be modeled by a simple wall model. As a first approximation of landing we use a ramp at the ground and show that the flow disturbances are similar to the result of flat ground with obstacles. In particular two kinds of so-called end effects are superposed: pressure waves in the vortex core and the propagation of the secondary vortex structures.