Unsteady aerodynamic response modeling: A parameter-varying approach

Current low-dimensional aerodynamic modeling capabilities are greatly challenged in the face of aggressive flight maneuvers, such as rapid pitching motions that lead to aerodynamic stall. Nonlinearities associated with leading-edge vortex development and flow separation push existing real-time-capable aerodynamics models beyond their predictive limits. The inability to accurately predict the aerodynamic response of an aircraft to sharp maneuvers makes flight simulation for pilot training unrealistic and, thus, ineffective at adequately preparing pilots to safely handle compromising flight scenarios. Inaccurate low-dimensional models also put practical approaches for aerodynamic optimization and control out of reach. In the present development, we make a push toward realizing real-time-capable models with enhanced predictive performance for flight operations by considering the simpler problem of modeling an aggressively pitching airfoil in a low-dimensional manner. We propose a parameter-varying model, composed of three coupled quasi-linear sub-models, to approximate the response of an airfoil to arbitrarily prescribed aggressive ramp-hold pitching kinematics. An output error minimization strategy is used to identify the low-dimensional quasi-linear parameter-varying sub-models from input-output data gathered from low-Reynolds number (Re = 100) direct numerical fluid dynamics simulations. The resulting models have noteworthy predictive capabilities for arbitrary ramp-hold pitching maneuvers spanning a broad range of operating points, thus making the models especially useful for aerodynamic optimization and real-time control and simulation.