INFLUENCE OF STRUCTURAL AND AERODYNAMIC MODELING ON FLUTTER ANALYSIS

The dynamic aeroelastic capabilities in the automated structural optim ization system were used to evaluate the flutter behavior of various f ully built-up finite element wing models in subsonic and supersonic fl ow. First, the performance of the flutter module was tested against re sults from other codes. Then, models of various wings with different a spect ratios were investigated for the influence on the free vibration and flutter characteristics of such modeling factors as finite elemen t selection, structural grid refinement, number of selected modes, ret ention of in-plane and breathing modes, aerodynamic panel size and pla cement, splining of the aerodynamic grid to the structural grid, selec tion of extra points off the structural wing box for splining, solutio n procedures such as eigenvalue extraction routines, reduction schemes , etc. The results suggest that a quick initial evaluation of a prelim inary wing design with a reasonably coarse grid for both the structure and the aerodynamics will result in natural frequencies and modes tha t are close to those from a more detailed model and in flutter speeds that tend to be conservative. Overall, such a simple model can represe nt a good start for a conventional redesign process as well as for opt imization.