An Aeroelastic Reduced Order Model for Dynamic Response Prediction to Gust Encounters

Abstract

The main contribution of this work is the development of a method which bridges the gap between the computational effort required by high-fidelity aeroelastic methods and the loss of accuracy of low-fidelity methods in transonic flow regimes. The aeroelastic Reduced Order Model (ROM) aims to predict not only the aircraft response to gust encounters but also the airframe loads as provided by higher fidelity methods. The method is shown for discrete vertical gust encounters but is applicable to any other atmospheric disturbance scenarios. The application of the method is especially interesting in aerodynamic regions where classical linear aerodynamic methods show modeling limitations. The method is based on the modification of the unsteady Aerodynamic Influence Coefficient (AIC) matrices and uses a small number of Computational Fluid Dynamics (CFD) reference computations. The so called aerodynamic correction modes conform the basis for the aerodynamic description of the aeroelastic ROM. An extension into the nonlinear aerodynamic region is done, where the aerodynamic effects due to the atmospheric perturbation and to the aircraft motion may not be superposed. Two methods are developed, one based on the concept of quasilinearization and another one including the quasilinearization and a linearization around a nominal trajectory. It is shown that for weak nonlinearities the quasilinearization method is able to properly describe the main nonlinear effects for the practical cases considered. The ROM is applied to a NACA64A010 profile in the transonic regime and applications to free flexible aircraft for different aerodynamic fidelity level models, namely Euler and RANS models, are further considered. A special focus is laid on the impact on the incremental cut loads acting over the airframe.