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.

Study of Paired Approach Wake Separation Based on Crosswinds

“…where lnk τ is the initial connection time of the wake vortex. The motion of the wake vortex accelerates after the formation of the irregular vortex ring, and this phase is primarily governed by long-term spontaneous diffusion induced by turbulence [30]. The lateral distance of the wake vortex with time is where bias t is the bias time and represents the moment when the longwave instability reaches the point of maximum amplitude.…”

Lagrangian Vortices Interactions Using Large-Eddy Simulation (LES) and Surface Roughness Model—Application for Aircraft Wake Vortices with Crosswind

“…The vortex Reynolds number defined in terms of circulation strength, Γ, and kinematic viscosity, ν, proves suitable for capturing this type physics [21]. The literature has reported that physics associated with the rebounding effect does not occur unless the viscous boundary layer condition is imposed on the runway [22][23][24][25][26]. Figure 8 shows the phenomena above interpreted including a crosswind velocity of magnitude U = 0.04 blowing the primary vortical structures.…”

“…The problem of the dissipation of aircraft vortex wakes has been the focus of extensive studies aiming to predict the potential hazard of wake vortices and their lifetime in the ground effect [22][23][24][25][26]. The air always flows from a region of high pressure to a region of low pressure, and in the case of the aircraft wing, air flows from below the wing to the upper surface of the wing.…”

Optimised Pairwise Aircraft Separation Minima Applying Plate Lines

“…Lidar measurements at Vienna airport showed that a Plate Line is able to effectively reduce the wake vortex lifetime [8], especially of the longest-living vortices. Also, a ight simulator study revealed that the faster decayed vortices reduce the severity of a wake encounter and increase the pilot acceptance of such disturbances [9]. Hence, the previous investigations showed the effectiveness of the plates to lower the risk of hazardous wake encounters in ground proximity and thus increase ight safety.…”