The effect of gusts on aircraft wake vortices

Abstract

Purpose-Aircraft wake vortices present a potential risk to following aircraft, particularly during final approach and landing, as wake vortices may remain in the flight corridor for a long time. Wind and turbulence are the key factors influencing the wake vortex evolution, but also the wake vortex generation at the aircraft. Flying through a gust influences the wake vortex roll-up process and its evolution. Note that vertical and lateral gusts may affect counterrotating wake vortices differently. Both vortices influence each other by inducing a downward velocity. Disturbances may therefore lead to local vortex tilting and later to a complex three-dimensional deformation. This work employs two different hybrid Reynolds-averaged Navier-Stokes/large-eddy simulation (RANS/LES) approaches to investigate the effect of gusts on wake-vortex evolution. In a one-way coupling a pre-calculated RANS velocity field of the aircraft's near-field is being swept through an LES domain. The effect of a sine gust on the turbulent wake is modelled by manipulating the RANS-field accordingly. As a more sophisticated approach the concept of a two-way coupling is being presented. Here an LES solver is bi-directionally coupled with an unsteady RANS (URANS) solver, exchanging values at every physical time step of the simulation. Design/methodology/approach-A one-way coupling approach of the LES code MGLET and the RANS code TAU is presented to simulate the gust effect on aircraft wake vortices. Additionally the concept of a two-way coupling of these two codes incorporating a coupling module. Findings-The gust effect of wake vortices subjected to a crosswind can be simulated. The vortex physics is analysed. Unexpected behavior like fast upwind vortex decay is revealed. Practical implications-The understanding of the aircraft wake vortex physics during landing provides valuable information for wake-vortex advisory systems. Originality/value-The effect of gust on wake vortices during and after landing has not been studied so far. The hybrid on-way coupling approach is relatively new, as well as the concept of the two way coupling.

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