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Aircraft Wake Vortex Evolution During Approach and Landing With and Without Plate Lines

As an unavoidable consequence of lift, aircraft generate a pair of counter-rotating and persistent wake vortices that may pose a potential risk to following aircraft. The highest risk to encounter wake vortices prevails in ground proximity, where the vortices cannot descend below the glide path but tend to rebound due to the interaction with the ground surface. Computational fluid dynamics simulations executed on GCS system SuperMUC of LRZ Garching are used to investigate the complex vortex system detaching from the aircraft wings in high-lift configuration which rolls up to a counter-rotating vortex pair (see Fig. 1 top left), via the interaction of the formed vortex pair with the ground surface (Fig. 1 bottom), up to the final vortex decay. The simulations indicate that so-called end effects are triggered by the sudden loss of lift during touchdown. Pressure disturbances propagate along the vortex centers leading to rapid vortex decay. Simultaneously, a vorticity layer is induced at the ground that is wrapped around the wake vortices and also contributes to vortex decay (Fig. 1 bottom). These mechanisms which advance quickly in ground proximity can be complemented at higher flight heights by the installation of plate lines at the runway tails. The plate lines induce smaller vortices that actively approach and propagate along the aircraft trailing vortices. In Fig. 1 bottom left, the decline of high velocities (indicated by reddish colors) at the plate line and the gap becoming visible at later times in Fig. 1 bottom right indicate the beneficial effects of the small plates erected on the airfield. The simulations and flight experiments conducted on 29 and 30 April 2013 at special airport Oberpfaffenhofen (see Fig. 2) indicate that the patented plate lines appreciably accelerate wake vortex decay and interfere favorably with end effects. This way safety can be further increased during the final approach -- the flight phase with most reported encounters. Future developments shall replace the currently stationary flow field around the aircraft assimilated into the computational domain by a fully unsteady solution for a landing aircraft. The plate line design needs to be further optimized regarding the application to aircraft of different sizes and the compatibility with airport requirements. Once criteria like obstacle clearance, stability, frangibility, interference with the localizer, requirements of wildlife, and grounds maintenance are resolved and approved by authorities, it is planned to demonstrate the functionality of the plate line concept in an operational environment at Munich airport.

Wake vortex evolution of a landing aircraft. © DLR OberpfaffenhofenFigure 1: Wake vortex evolution of a landing aircraft from vortex roll-up until final decay triggered by the interaction with the ground surface and a plate line installed in the prolongation of the runway. High velocities red, low velocities white.
Copyright: © DLR, Oberpfaffenhofen (Germany)

Wake vortex evolution of a landing aircraft. © DLR OberpfaffenhofenFigure 2: Overflight of DLR research aircraft HALO and vortex roll-up in ground proximity visualized by smoke at special airport Oberpfaffenhofen.
Copyright: © DLR, Oberpfaffenhofen (Germany)

Full article in inSiDE, Vol. 11 No. 2

Frank Holzäpfel and Anton Stephan
German Aerospace Center (DLR)
Institut für Physik der Atmosphäre
Münchner Straße 20, D-82234 Weßling - e-mail: Frank.Holzaepfel@dlr.de

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