Dynamic response of an aeroelastic airfoil within ground effects of flat and wavy surfaces

Due to the significant threat posed by waves to the safety of ground-effect vehicle, a numerical study has been conducted to reveal the impact patterns on the dynamic response of an aeroelastic airfoil flying above flat and wavy ground surfaces compared with the case of in far field. The two degrees of freedom dynamic equations are coupled with the governing equations of incompressible flow with the Reynolds number based on a chord length of Re=6.85×107. The airfoil is capable of pitching and plunging motions driven by both elastic and aerodynamic forces. The effects of spring stiffness and damping ratio on aeroelastic flutter of the airfoil are explored within flat ground effect and wavy ground effect conditions, respectively. Compared to the airfoil in the far field, the aeroelastic airfoil exhibits better stability within the flat ground effect. Within the ground effect of flat surface, as the spring stiffness decreases, the dynamic response of the airfoil can be categorized into four different types: static state (U*=5, 6, and 7), limit cycle oscillation (U*=8), nonlinear random oscillation (U*=9), and stall-induced collision with the ground (U*=10). When flying above waves, the airfoil experiences sustained wave excitation, resulting in intensified velocity fluctuations and increased susceptibility to collision with ground. The effectiveness of damping in mitigating flutter and preventing crashes is demonstrated for airfoils within the ground effect. These findings provide valuable insights into the risks associated with aeroelastic flutter of the airfoil within the ground effect, offering implications for the safety design of wing-in-ground vehicles.