Aeroelastic modeling and analysis of wings considering geometric nonlinearity

Flexible wings with high aspect ratio are widely used in high-altitude and long-endurance Unmanned Aerial Vehicles (UAVs) because of low structural weight and high aerodynamic lift-to-drag ratio. This kind of wings experience large geometric deformation in flight, and the linear structure model based on small deformation hypothesis is no longer applicable. Therefore, it is necessary to build the structure model which can simulate geometric nonlinearity. Based on the Newtonian method, the dynamic equations for the geometric non-linear structure model are derived, which can be mutually validated by and complemented with the method based on Hamilton's principle derived by Hodges. To simulate the aerodynamics of flexible wings more precisely, a model for three-dimensional unsteady aerodynamics, which can consider large deformation of the wing, is built. Based on the nonlinear structure model and the unsteady aerodynamic model, the nonlinear aeroelastic model is built through loose coupling. The precision of the aeroelastic model is verified through tests. The results show that the flutter speed of flexible wings is sensitive to the free-stream angles of attack and span-wise length. When the free-stream speeds exceed the flutter speed, the wing's vibrations are stable Limited Cycle Oscillations (LCO) rather than divergence. However, as the free-stream speeds continues increasing, the wing's vibrations converge again and the damping turned to be positive.