Study of four-vortex aircraft wakes and layout of corresponding aircraft configurations

A sequence of numerical simulations for the efficient determination of four-vortex wakes, consisting of two counter-rotating vortex pairs, with low induced rolling moments after the unstable merging of inner and outer vortices, is proposed. After a systematic investigation of generic four-vortex systems in a second step, an airliner geometry in high-lift configuration is modified such that it produces a vortex wake similar to the identified optimal four-vortex system. The configuration modification is done using simple design rules. For verification of the existence of a similar four-vortex system, the wake vortex of the modified airliner configuration is simulated up to the extended near field in a final step. Two four-vortex configurations are considered in the present paper, different only in the vortex spacing ratio. A maximum reduction of rolling moment down to 44-52% of the rolling moment of a reference two-vortex system is achieved within a distance equivalent to 2.89 n miles for a real size Airbus A340. The realization of four-vortex wakes behind an individually modified high-lift configuration similar to the aforedetermined promising generic four-vortex configurations is demonstrated.