Flow-induced vibrations of a pitching and plunging airfoil

The flow-induced vibration (FIV) of an airfoil freely undergoing two-degrees-of-freedom (2-DOF) motions of plunging and pitching is numerically investigated as a function of the reduced velocity and pivot location in a two-dimensional free-stream flow. This investigation covers a wide parameter space spanning the flow reduced velocity range of 0 <U^∗=U/(f_nc) ≤ 10 and the pivot location range of 0 ≤ x ≤ 1, where U is the free-stream velocity, f_n is the natural frequency of the system set equal in the plunge and pitch directions, c is the chord length of the foil and x is the normalised distance of the pivot point from the leading edge. The numerical simulations were performed by employing an immersed boundary method at a low Reynolds number (Re = Uc/v = 400, with v the kinematic viscosity of the fluid). Through detailed analyses of the dynamics of the 2-DOF vibrations and wake states, a variety of FIV response regimes are identified, including four regions showing synchronisation or near-synchronisation responses (labelled as S-I, S-II, S-III and S-IV) and four transition regimes (labelled as T-I, T-II, T-III and T-IV) that show intermittent, switching or chaotic responses, in the x-U^∗space.