Study of a C-wing configuration for passive drag and load alleviation

Non-planar wing configurations are often hypothesised as a means for improving the aerodynamic efficiency of large transport aircraft; C-wings may have the ability to exploit and unify drag reduction, aeroelasticity, and dynamics and control but their capacity to do so is ambiguous. The aim of this work is to provide an experimental demonstration with the aim of verifying the C-wing configuration’s potential application for drag and load alleviation. The successful application of a C-wing system for improving the aerodynamic efficiency depends upon the ability to construct the wing system such that a sufficiently low root bending moment and parasitic drag is maintained, relative to an equivalent planar wing system. This was facilitated by the development of a structured genetic algorithm (sGA) optimisation architecture capable of utilising fundamental aerodynamic theory, design specifications, and experimental facility constraints to provide non-arbitrary wing topology designs. The optimisation procedure aided in the design of a planar wing analogous of a typical mid-sized transport commercial aircraft wing topology, representing a 10% scale model. From this baseline design the sGA reconfigured the outboard 26% of the wing to independently form a C-wing topology, increasing the planforms aerodynamic efficiency by 74.5%. A modular wingtip semi-span model was designed to house the sGA planar and Cwing designs inside the University of Glasgow’s de Havilland wind tunnel for tests at Re = 1.5x10^6. A number of experimental techniques adopted, such as force/moment measurements, laser-Doppler vibrometry, PCB piezoelectric accelerometry, direct image correlation (DIC), surface flow visualizations, and stereoscopic particle image velocimetry (SPIV), provide insight into the semi-span model and wingtip arrangement structural dynamics and flow field physics. Aerodynamic performance metrics show that despite the C-wing operating with a 19.1% higher wing wetted area, a peak total drag reduction of 9.5% at a = 6^o is achieved in addition to a 1.1% reduction in the wing root bending moment for equivalent lift. Study of the near field wake indicated that this was achieved by the C-wing establishing a low vorticity spiral core vortex with accelerated vortex decay properties. The C-wing has also been found capable of passively attenuating buffet induced vibrations of the main-wing by up to 68.6%