Investigation of two degrees of freedom on vortex-induced vibration under the wake interference of an oscillating airfoil

For the two-degree of freedom (2-DOF) VIV in the wake of the steady flow, seven types of the phase portraits of the displacement shapes are observed. In the range of small reduced velocity (Vr<5), the body trajectories are mainly characterized by an “8-shape” with some differences in phase. At the peak amplitude, the body trajectories have changed into two shapes: i.e., the half “8-shape” (initial stage) and the crescent-shape (final stage). When Vr=6, the body trajectories have also shown to have two shapes: i.e., the “8-shape” (initial stage) and the half “8-shape” (final stage). When Vr arrives at the low branch (Vr>7), the body trajectories will become irregularly shaped like a cone-net.