Aerodynamic and Aeroelastic Behavior of Wings in the Presence of Upstream Vortical and Viscous Disturbances

The objective of the research was to study the effect of upstream flow disturbances on the unsteady aerodynamics and aeroelastic behavior of a downstream wing. A wind-tunnel aeroelastic apparatus, consisting of an elastically-supported airfoil with an optional upstream bluff-body flow-disturbance generator, was developed. The experimental results show that the flow disturbances cause amplitude modulation of an otherwise constant-amplitude limit-cycle oscillation (LCO) of the airfoil. Annihilation of LCO was demonstrated under certain conditions. This is believed to be the first experimental demonstration of the annihilation of an aeroelastic LCO. A new ``aeroelastic inverse'' algorithm, based on inverting the equations of motion to solve for the lift and moment experienced by an aeroelastic wing, was developed to better understand the LCO modulation. The results show that the pitch-heave mass coupling, which affects the pitch-heave phase difference, controls the amplitude modulation. A new gust generator, that allows for control of the phase of the shed vortices, was designed using computational fluid dynamics. With this gust generator, LCO modulation and annihilation have been demonstrated by open-loop control of the gust-generator oscillation. A low-order prediction method was developed for studying the effects of upstream flow disturbances on the unsteady aerodynamics of a prescribed-motion airfoil. The flow disturbances were seen to modify LEV shedding, the details of which depend on the amplitude and phase of the disturbance relative to the airfoil motion.