A simulation case-study on the influence of plate lines on the severity of wake vortex encounters in ground proximity

Kurzfassung

Close to ground the behaviour of wake vortices changes in comparison to out of ground effect. Whilst vortices descend in free air due to their mutual induced velocities, they are hindered in sinking in presence of ground. This also changes the risk to encounter the wake of a preceding aircraft. Furthermore, wake encounters in ground effect are especially critical due to the nearness of the ground. Recent studies showed that vortex decay in ground proximity can be accelerated by installing a series of plates in lines perpendicular to the flight direction (so-called plate lines). This study analyses whether the accelerated vortex decay also results in lesser encounter severity in terms of aircraft reaction and pilot acceptance. Flow fields were generated by coupled RANS-LES simulations of an A340-sized aircraft in ground effect with light crosswind with and without plate lines for different vortex ages were implemented in a six-degrees-of-freedom aircraft simulation of an A320-sized aircraft. Offline simulations with autopilot engaged in autoland-mode showed a significant reduction of the aircraft response during the wake encounter with the plate lines. This reduction is indeed more pronounced with younger vortices but is still noticeable with old vortices. Simulations with pilots-in-the-loop in a full-flight simulator applying the same simulation model for the encountering aircraft also show a reduction of the aircraft response during manual landing as well as improved subjective pilot acceptance. Plate lines are therefore considered an effective means for either increasing flight safety with current minimum separations or maintaining the same level of safety in case that the minimum separations are reduced in the future.