Scaling unsteady load alleviation in airfoils with flexible trailing-edges

Unsteady load alleviation is crucial for engineering applications such as tidal turbines. Herein, we present an experimental study into the load alleviation capacities of constantsection 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 Re = O(104 ). To quantify the role of airfoil flexibility, we introduce two Cauchy numbers (Cau and Cav ), 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 semiempirical 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.