Nonlinear Aeroelastic Modeling of a Flexible Wing and Comparison with Experiments

Abstract

A wind tunnel experimental investigation of limit cycle oscillations (LCO) of a uniform flexible airfoil with root pitch motion occurring at transitional Reynolds number regime (4.5×10 4 ≤ Re c ≤ 1.3 × 10 5 ) is presented. Depending on the initial conditions, two stable limit cycle regimes are observed: small and large amplitude LCO. The origin of the large amplitude LCO is determined to be coalescence flutter for which the exponential growth of the amplitude is limited by the stall at large angles of attack. On the other hand, the small amplitude LCO are attributed to laminar boundary layer separation related to transitional Reynolds number aerodynamics. In addition, the nonlinear equations of motion for a cantilever is developed considering chordwise and flapwise bending, torsion and base rotation. The nonlinearities arise from two main sources: the structural flexibility and the coupling of the bending and torsional motions with the base rotation. Furthermore, a linear inviscid aerodynamic model is considered using both quasisteady and unsteady forcing terms. Despite the linear aerodynamics approximations, a parallel to the experiments can be drawn with the numerical simulations presented for small and large amplitude LCO at the vicinity of the linear flutter speed, with a dominant cause factor being a coalescence flutter.Overall, the structural nonlinearities play significant role in LCO for both the experimental and numerical investigations.ii