| Résumé | The present study investigates the nonlinear feedback coupling mechanism between unsteady low-Reynolds-number aerodynamics and structural response. Structural-response models addressing one-degree-of-freedom and two-degrees-of-freedom aeroelastic oscillations were coupled with an in-house-developed computational fluid dynamics code to perform large-eddy simulations for flows past a rigid airfoil in free-to-rotate and free-to-rotate-and-heave conditions at a low Reynolds number. As observed in the experiments, the numerical simulations confirmed the presence of self-sustained low-amplitude limit-cycle oscillations of a NACA 0012 airfoil. It was understood that this behavior in the transitional Reynolds-number regime resulted from the unsteadiness of the laminar boundary-layer separation and its delayed recovery when compared to the corresponding static conditions. The feedback coupling mechanism between the laminar-separation-bubble behavior and the structural response caused negative aerodynamic damping; thus, the aerodynamic forces did positive work and fed energy from the flow to the airfoil, sustaining the low-amplitude aeroelastic oscillations. The amplitude in pitch of the limit-cycle oscillations was of the order of 5-7 deg. As the operating angles of attack in unmanned-air-vehicle flights are within close range of the limit-cycle-oscillation occurrence, understanding and controlling the limit-cycle oscillation of the wings could ensure unmanned-air-vehicle stability so that it could acquire high-quality camera images and other data, for instance. Copyright © 2013 by Christopher Porter, R. Mark Rennie, Eric J. Jumper. |
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