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

Gust disturbances pose a fundamental aeroelastic challenge for the lightweight, high-aspect-ratio flexible wings, particularly in solar-powered aircraft applications. This study experimentally investigates gust alleviation on a flexible cantilevered wing (aspect ratio = 9.4) subjected to periodic gust excitations at frequencies ranging from fg=0.5 to 4 Hz. Wind tunnel tests were conducted at a constant freestream velocity of U∞=10.0 m/s (chord-based Reynolds number Rec=5.88×104). Bending and torsional deformations are quantified using Digital Image Correlation, while forces and moments at the wing root are measured with a load cell, and flow fields are captured via Particle Image Velocimetry. The results reveal a pronounced beating response under gust excitation at half the natural torsional frequency (fg/fn,θ=0.5), characterized by cyclic divergence-decay oscillations in both bending and torsion, leading to significant aerodynamic load fluctuations. To mitigate these gust disturbances, a structurally designed multistable shell was developed and applied on the wing section from 0.71 to 0.92 wing span. Under gust loading, the multistable shell can passively morph the wing configuration, resulting in an immediate reduction in root loads and suppression of the beating response. Flow field analysis reveals that the passive shape morphing of the multistable shell suppresses dynamic stall behavior, thereby decoupling the lock-in phenomenon between the structural torsional vibrations and the coherent dynamic stall vortices shedding, which is a key energy transfer mechanism driving the beating response. The multistable wing also demonstrates control effectiveness across other gust frequencies by reducing structural vibrations and root loads.