Efficient aeroelastic analysis using unstructured CFD method and reduced-order unsteady aerodynamic model

Flutter computations are presented for the AGARD 445.6 wing model and the Wing-Pylon-Nacelle configuration model using a fully implicit aeroelastic unstructured-mesh Euler solver coupled with a linear structural dynamics solver and Reduced-Order Model (ROM) based on the Volterra theory. The ROM is used for the rapid evaluation of nonlinear generalized unsteady aerodynamic forces (GAFs) both in a time-domain and a frequency-domain. The convolved time-domain GAFs agree well with direct computation results, and the frequency-domain GAFs at distinct values of reduced frequency are computed from the time-domain GAF responses to unit-amplitude harmonic excitation of elastic modes using a simple convolution scheme. The frequency-domain GAFs are processed using the Roger's approximation method in order to generate an unsteady aerodynamic state-space ROM, which is used for creating an aeroelastic state-space model. The aeroelastic state-space model is solved as a complex eigenvalue problem using MATLAB's® Toolbox to obtain V-g plots. The ROM-based flutter analysis is rapid and yields accurate results compared with experiment, direct simulation results and linear aerodynamics results by MSC/NASTRAN.