Simulation study of severity and mitigation of wake-vortex encounters in ground proximity

Abstract

Wake-vortex encounter reports as well as simulations show a significantly higher encounter probability during landing shortly before touchdown in comparison to other flight phases. This is caused, among other factors, by the special behavior of wake vortices in ground effect. Nevertheless, hazardous wake encounters with adverse consequences are rarely reported in reality. To gain more insight in the mechanisms of wake encounters close to ground, encounter simulations were performed with realistic vortex flowfields. These were generated using coupled Reynolds-averaged Navier-Stokes and large-eddy simulations covering the whole vortex evolution in ground effect from generation until decay and were used for a hazard analysis. Encounter simulations were performed with a simulation model of an A320-size aircraft with autopilot engaged following an A340-size aircraft. Different wind conditions and vortex ages were considered as well as a so-called plate line. Recent studies showed increased vortex decay when a series of plates is positioned in front of the runway threshold. The results of the study reveal a significant reduction of the maximal vortex impact on the encountering aircraft due to the plate line. This effect is more pronounced for younger vortices, but also for operationally relevant vortex ages, a considerable effect of the plate lines in reducing the maximum aircraft reaction due to a wake encounter close to ground can be observed.