N.L.M. van Luijk
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2 records found
1
The Reynolds Number Effect on the Flow Topology on a Flying V Aircraft
A Numerical Investigation
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.
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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.
The aviation industry is exploring unconventional aircraft designs like the Flying V in its drive to reduce carbon emissions and improve fuel efficiency. The Flying V, featuring a crescent wing with leading edge kink, currently suffers from an unstable nose-up pitch tendency. This study investigates vortex control methods within this kink region to increase lift on the outboard wing and delay the pitch-break. A full-span, modular wind tunnel model is used to investigate the effects of parabolic and diamond juncture fillets, as well as full-chord fences, on the pitching moment characteristics. Stereoscopic Particle Image Velocimetry (SPIV) and oil flow visualization are used to analyse vortex behaviour and flow topology. Results reveal that the parabolic fillet outperforms the diamond fillet in generating lift at higher angles of attack due to its ability to promote vortex formation and delay breakdown. The installation of full-chord fences increases lift on the outboard wing and positively influences the pitching moment, though none of the tested configurations increased the pitch-break angle.
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The aviation industry is exploring unconventional aircraft designs like the Flying V in its drive to reduce carbon emissions and improve fuel efficiency. The Flying V, featuring a crescent wing with leading edge kink, currently suffers from an unstable nose-up pitch tendency. This study investigates vortex control methods within this kink region to increase lift on the outboard wing and delay the pitch-break. A full-span, modular wind tunnel model is used to investigate the effects of parabolic and diamond juncture fillets, as well as full-chord fences, on the pitching moment characteristics. Stereoscopic Particle Image Velocimetry (SPIV) and oil flow visualization are used to analyse vortex behaviour and flow topology. Results reveal that the parabolic fillet outperforms the diamond fillet in generating lift at higher angles of attack due to its ability to promote vortex formation and delay breakdown. The installation of full-chord fences increases lift on the outboard wing and positively influences the pitching moment, though none of the tested configurations increased the pitch-break angle.