Unsteady load alleviation is crucial for engineering applications such as tidal turbines. Herein, we present an experimental study into the load alleviation capacities of constant-section airfoils with flexible trailing-edges. The trailing-edge studied here consists of two independent flexible skins, enabling large skin deformations and enhanced load alleviation compared to conventional flexible trailing-edge designs. We test high-amplitude plunging kinematics (up to peak-to-peak amplitude of one chord length) at reduced frequency $k=0.2$ and Reynolds numbers $\mathrm{Re}=\mathcal{O}\left({10}^4\right)$. To quantify the role of airfoil flexibility, we introduce two Cauchy numbers (${\mathrm{Ca}}_u$ and ${\mathrm{Ca}}_v$), which normalize the freestream and plunging velocities, respectively. We demonstrate that both the trailing-edge deflection and the resulting lift alleviation scale with these Cauchy numbers provide a fundamental framework for understanding flexible airfoil dynamics. Furthermore, we propose semi-empirical models for unsteady lift alleviation, which agree with our measurements. These findings lay the groundwork for fully predictive low-order models, advancing the design of passively morphing airfoils for efficient load control in unsteady flow environments.

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• Aerodynamics
• Flow-structure interactions