Modeling Wake Vortex Roll-Up and Vortex-Induced Forces and Moments for Tight Formation Flight

Abstract

Migratory birds that fly in tight formation use the upwash of the leading birds to save energy. Aircraft can use the same principle to save fuel. To date, commercial aircraft do not fly in tight formation because of unresolved technical and operational issues. However, increasing fuel cost and environmental constraints are drivers to investigate tight formation flight and the potential fuel savings. For such investigations a good knowledge of the vortexinduced velocities and the effect on the encountering aircraft is fundamental. In research on safe separation distances the vortex far field (more than 40 wingspans behind the generating aircraft) is modeled with a pair of straight vortices. This paper addresses a method to model the wake vortex roll-up that occurs in the near field (up to 15 wingspans behind the generating aircraft) using discrete vortex filaments. The motion of these filaments due to the mutual velocity induction is simulated numerically, followed by the calculation of the resulting induced velocities in a second step. To find an appropriate set of simulation parameters, the computed velocities are compared with those induced by a validated wake vortex velocity model. An already existing wake vortex encounter simulation software is improved to model the wake vortex roll-up. First simulation results are presented.