Aeroelastic Indicial Response Reduced-Order Modeling for Flexible Flight Vehicles

A reduced-order modeling method capable of providing computationally efficient predictions of the nonlinear, unsteady aerodynamics encountered by flexible flight vehicles is presented. Models are developed using the indicial response theory, which characterizes a vehicle's dynamics through identification of time-accurate aerodynamic responses due to step changes in vehicle-state motion parameters. A coupled computational fluid dynamics aeroelastic analysis is proposed for identifying flexible vehicle step responses. In this approach, aeroelastic indicial responses are simulated via prescribed rigid-body motions, whereas fluid-structure interactions are captured at the subiterative level through coupling to a modal structural solver. A nonlinear extension of the indicial response theory is applied through time-dependent interpolation of a database of locally linear aeroelastic step responses as a function of angle of attack. Reduced-order models are created using the mathematical principle of convolution to predict the time-dependent aerodynamics of a flexible vehicle subject to arbitrary prescribed trajectories. The NASA FUN3D computational fluid dynamics solver is used for simulating trajectories and indicial response functions. Aerodynamic predictions were generated for the flexible X-56A aircraft undergoing a series of forced oscillations. The reduced-order modeling solutions are shown to provide a practical option for evaluating the unsteady aerodynamics of flexible vehicles using high-fidelity simulations.