The effect of gusts on aircraft wake vortices – one-way and two-way coupling of RANS and LES codes

Abstract

Aircraft wake vortices present a potential risk to following aircraft, particularly during final approach and landing, as wake vortices may remain in the air lane for a long time. Wind and turbulence are the key factors influencing the wake vortex evolution, but also the wake vortex generation behind the aircraft. Flying through a gust influences the wake vortex roll-up process and its evolution. Note that vertical and lateral gusts may affect counter-rotating wake vortices differently. Both vortices influence each other by inducing a downward velocity. Disturbances may therefore lead to local vortex tilting and later to complex three-dimensional deformation. This work employs two different hybrid 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 two-way coupling is being presented. Here an LES and a URANS solver are coupled bi-directionally, exchanging values at every physical time step.