Subcritical and supercritical nonlinear aeroelastic behavior of a morphing wing with bilinear hinge stiffness

Abstract A morphing wing with structural nonlinearities may encounter complex nonlinear oscillations during the in-flight morphing process. This paper investigates the nonlinear aeroelastic vibrations of a folding wing with bilinear stiffness in its hinge joints. The parameterized-fictitious-mode method is used to compute the nonlinear aeroelastic response of the morphing wing [as a subcritical or supercritical limit-cycle oscillation (LCO)] efficiently at different folding angles without having to perform repeated finite-element modeling. A low-aspect-ratio morphing wing is selected as a test case to investigate the nonlinear oscillations, and how the hinge stiffness and folding angle affect the nonlinear aeroelastic behavior is also investigated efficiently. The numerical results show that the nonlinear aeroelastic behavior of the folding wing is very complex. For a folding wing with sufficiently strong nonlinearity, the flight region of nonlinear oscillations is above the flutter boundary, and benign LCOs occur at flow speeds higher than the flutter speed. As the hinge stiffness is decreased, the region moves downward and is eventually entirely below the flutter boundary, whereupon detrimental LCOs occur at flow speeds lower than the flutter speed.