Nonlinear gust response of a control surface with free-play
Computational and experimental studies are conducted to investigate nonlinear aeroelastic responses of a typical airfoil section with control surface free-play excited by gust loads with various initial pitch angles. The experimental study has been conducted in the Duke University wind tunnel facility that is equipped with a rotating slotted cylinder gust generator. The experimental results show that if a ratio of initial pitch angle to the half free-play gap is held constant, the corresponding scaled non-dimensional response becomes nearly independent of the free-play angle. This indicates that a scaling law can be developed. Furthermore, both wind-tunnel and computational results show that at the zero angle-of-attack condition, i.e. when the airfoil is unloaded, limit cycle oscillation can occur over a wide range of velocities. However, when the angle of attack is increased, the range of the velocity within which the Limit Cycle Oscillation occurs becomes narrower. When the angle-of-attack is increased sufficiently, the limit cycle oscillation disappears. This indicates that if the control surface is sufficiently loaded, limit cycle oscillations due to the free-play effects can be completely eliminated. The computational results agree fairly well with the wind tunnel measurement indicating that the computational method is an accurate aeroelastic simulation method that can be adopted for nonlinear limit cycle oscillation and gust response with free-play nonlinearity.
