Nonlinear aeroelastic metastructure for wing flutter enhancement: modeling, simulation and wind tunnel experiment

To enhance aeroelastic stability in aircraft lifting surfaces, this study proposes a novel nonlinear metastructure wing (NMW) integrated with clearance-type nonlinear resonators (CNRs) for passive flutter suppression, addressing limitations inherent in conventional nonlinear stiffness designs. Each CNR comprises a cantilever-beam resonator and two pairs of symmetrically distributed cantilever beams, generating tunable non-smooth nonlinear stiffness enabled by adjusting the piecewise stiffness ratio and clearance size. An aeroelastic model of a long-straight wing coupled with clearance-type nonlinear metastructure in subsonic flow is developed, employing unsteady aerodynamic model based on subsonic lifting surface theory with minimum state approximation. The influence mechanisms of CNR structural parameters and distributions on linear flutter stability and post-flutter response behaviors are elucidated. Results demonstrate that tuning the CNR fundamental frequency induces distinct flutter coupling patterns, with an optimal design frequency maximizing the stability boundary of limit cycle oscillations for the NMW. A multi-frequency resonator design strategy of CNRs is further developed to simultaneously suppress multiple flutter instability modes, substantially improving the aeroelastic stability margin. Notably, the NMW with low-added-mass CNRs (adding approximately 8% mass) achieves significant post-flutter vibration reduction and a 49.4% enhancement in aeroelastic stability. Furthermore, wind tunnel tests further validate an approximate 40% increase in aeroelastic stability boundary compared to the baseline wing, demonstrating good agreement with theoretical predictions. This work establishes clearance-type nonlinear metastructure as an effective approach for passive flutter suppression in aircraft wings.