The Reynolds Number Effect on the Flow Topology on a Flying V Aircraft

Abstract

Over the past decades, a plateau has been reached in the development of conventional civil aviation passenger aircraft. To achieve significant improvements in efficiency, the aviation industry must investigate unconventional aircraft designs, such as flying wings, which are characterized by a blunt-nosed, highly swept cranked wing. These unconventional configurations can offer more than 10% improvement in cruise performance. At low speeds and high angles of attack, however, these wings exhibit complex vortical flow phenomena and may experience a pitch break, in which the aircraft becomes statically unstable about the pitch axis. Because previous studies mostly focused on wind-tunnel-scale models, this study investigates the effect of Reynolds number on vortex flow features at high angles of attack. Steady-state Reynolds Averaged Navier Stokes (RANS) simulations were performed at both sub- and full-scale Reynolds numbers using the generalized k-ω (GEKO) turbulence model. The results indicate two different flow mechanisms underlying the pitch break phenomenon: vortex lift-off at the sub-scale Reynolds number, and outboard wing flow separation combined with vortex breakdown at the full-scale condition. The findings show that higher Reynolds numbers postpone the onset of pitch break to higher angles of attack, extending the usable flight envelope compared to the sub-scale case.