ON THE FLUTTER MECHANISM DRIVEN BY SECOND BENDING-FIRST TORSION COUPLING IN HIGH-ASPECT RATIO WINGS

The present work investigates the flutter mechanism driven by second bending (B2)-first torsion (T1) modal coupling in high-aspect-ratio wings through wind tunnel experiments and a reduced-order aeroelastic model. Two taut-strip wings sharing the same airfoil profile but differing in structural properties are tested in two low-speed wind tunnels. Despite their geometrical similarity, the two wings exhibit significantly different aeroelastic behaviours: one undergoes flutter while the other remains stable, both displaying a hump-shaped damping variation characteristic of B2-T1 coupling. A Rayleigh-Ritz structural formulation coupled with Theodorsen's unsteady aerodynamics is validated against experimental frequency and damping trends. The spanwise distribution of aerodynamic work density shows that the vibration node of the second bending mode separates regions of energy input and dissipation, and that a strong dissipative contribution near the wing tip promotes the hump-mode restabilisation. Examination of the modal content indicates that a greater participation of the first bending mode enhances the bending-torsion energy exchange, thereby favouring flutter onset.