Prediction of Flutter Boundary of a Full Aircraft using a CFD-Based Reduced Order Method

The F-16 aircraft has a well-documented history of exhibiting limit-cycle oscillations (LCOs) under specific configurations and flight conditions, motivating extensive aeroelastic research using this platform. In this study, an open-source F-16 configuration is analyzed using a time-accurate, computationally efficient CFD-based approach to predict flutter boundaries and associated LCOs. A nonlinear fluid modal method is introduced to reduce the fully coupled aeroelastic problem into a second-order multi-degree-of-freedom (DOF) system while retaining essential nonlinearities and modal interactions. The method enables direct extraction of nonlinear fluid modal mass, damping, and stiffness from CFD solutions and formulates them into a system of ordinary differential equations (ODEs), eliminating the need for repeated CFD/CSD simulations. Application to the F-16 configuration demonstrates that the method can predict flutter boundaries with high accuracy at a fraction of the computational cost of conventional approaches.