Nonlinear inviscid aerodynamic effects on transonic divergence, flutter, and limit-cycle oscillations

By the use of a state-of-the-art computational fluid dynamic (CFD) method to model nonlinear steady and unsteady transonic flows in conjunction with a linear structural model, an investigation is made into how nonlinear aerodynamics can effect the divergence, flutter, and limit-cycle oscillation (LCO) characteristics of a transonic airfoil configuration. A single-degree-of-freedom (DOF) model is studied for divergence, and one- and two-DOF models are studied for flutter and LCO. A harmonic balance method in conjunction with the CFD solver is used to determine the aerodynamics for finite amplitude unsteady excitations of a prescribed frequency. A procedure for determining the LCO solution is also presented. For the configuration investigated, nonlinear aerodynamic effects are found to produce a favorable transonic divergence trend and unstable and stable LCO solutions, respectively, for the one- and two-DOF flutter models.