Gust alleviation of a high-aspect-ratio flexible wing by passive shape morphing via a multistable shell

The aerodynamic performance and structural safety of high-aspect-ratio flexible wings, such as those used in high-altitude long-endurance solar-powered unmanned aerial vehicles, are sensitive to gusts. This study aims to experimentally demonstrate gust alleviation through passive morphing using a multistable shell on a high-aspect-ratio flexible wing. The wing is a cantilevered NACA0012 configuration with an aspect ratio of 9.4, tested under an unsteady freestream velocity ranging from 9.3 m / s to 17.4 m / s . The chord-based Reynolds number (Re_c) ranges from 5.48 × 10⁴ to 1.02 × 10⁵. Bending and torsional deformations are quantified using Digital Image Correlation (DIC), while forces and moments at the wing root are measured with a load cell, and flow fields are captured via Particle Image Velocimetry (PIV). The results indicate that the wing experiences significant three-dimensional deformations and undergoes stall flutter under streamwise gust disturbances, resulting in substantial fluctuations in aerodynamic loads at the wing root. A structurally designed multistable shell is developed and applied on the wing section from 0.71 to 0.92 wing span. In the gust condition, the multistable shell can passively morph the wing configuration as a result of the aerodynamic loads, immediately leading to a reduction in aerodynamic loads and a suppression of structural vibrations. Flow field analysis reveals that the passive shape morphing of the multistable shell inhibits the flow separation at the leading edge so that the dynamic stall behavior is fully suppressed. This finding indicates that this passive shape morphing technique via a multistable shell is capable for flutter suppression of flexible wings in gusts.