Reduced-order-model approach for aeroelastic analysis involving aerodynamic and structural nonlinearities

A reduced-order model (ROM) for solving an aeroelasticity problem including structural and aerodynamic nonlinearities is introduced. The aerodynamic system is identified using a Volterra-based ROM. The appropriate procedures needed for the identification of the aerodynamic linearized kernel are presented, and a procedure to identify the first- and second-order Volterra kernels and a linearized ROM kernel from aerodynamic step response is detailed. A coupled framework for addressing the nonlinear aeroelasticity problem using a typical wing section model is introduced for the validation of the procedure. Nonlinear unsteady aerodynamic forces in both subsonic and transonic regimes are evaluated using a conventional approach using the CFL3D (version 6.1) code capable of integrating Navier-Stokes and the structural equations. The computational-fluid- dynamics (CFD) solver is used to compute the aerodynamic response to step or impulse inputs. Aerodynamic responses to arbitrary inputs are predicted using ROM kernels. The Gaussian pulse response obtained using ROM was validated by comparison with the response obtained from CFD solver. Aeroelastic analysis was conducted using the ROM with aerodynamic and structural nonlinearities. The results show that the reduced-order model can estimate accurately flutter speed as well as the limit-cycle oscillations (LCO). Also the ROM approach is found to be computationally efficient.