Nonlinear-Model-Inversion Control for Stall-Flutter Suppression of an Airfoil via Camber Morphing

Abstract

This paper presents a nonlinear-model-inversion control law to suppress stall flutter of an airfoil with active trailing-edge morphing. First, a nonlinear aeroelastic model is proposed utilizing two nonlinear autoregressive neural networks with exogenous inputs , which are used to predict aerodynamic moments on an airfoil due to large-amplitude oscillation and camber morphing, respectively. Afterward, a nonlinear-model-inversion control system is designed upon the mentioned aeroelastic system to suppress stall flutter via the camber morphing. A fluid–structure–control (FSC) coupling strategy is developed with structure and control systems embedded in the high-fidelity computational-fluid-dynamics environment to validate the control effect. The FSC high-fidelity simulations show that the nonlinear-model-inversion controller can suppress pitching oscillation completely, whereas a linear proportional–derivative controller without time delay only performs a limited suppression rate by 25.6%. The flowfield evolution result infers that the active camber morphing can generate a converse training-edge vortex, which counteracts the leading-edge vortex during stall flutter. From the perspective of an energy hysteresis, active camber morphing works well by converting injected aerodynamic energy from positive to negative.