Numerical Investigation of Wing Section Undergoing Low-Frequency Aeroelastic Limit Cycle Oscillations

Abstract

An in-house-developed computational fluid dynamics code that allows for grid motion was implicitly coupled with the differential equation for a harmonic oscillator. Simulations were carried out for a wing section with an airfoil from the X-56A with a chord-based Reynolds number of and 12 and 15 deg angles of attack. Results for 12 deg angle of attack show that for a wing section with low inertia and highly flexible support, the amplitude of the structural motion of the wing section motion is relatively weak. For a wing section with higher inertia and stiffer support, the structural response matches the natural eigenfrequency. For both cases, compared with results for the rigid (nonmoving) wing section, the frequency content of the aerodynamic loads is noticeably reduced near the structural eigenfrequency. For the wing section with stiffer support at 15 deg angle of attack, a laminar separation bubble is repeatedly bursting and reestablishing itself at a relatively low frequency. When the stiffness of the support is reduced so that the low-frequency of the bubble bursting couples with the structural eigenfrequency, the amplitude of the unsteady aerodynamic forces is doubled and the amplitude of the structural motion increases nearly 30 times compared with the stiffer support.