Numerical study of vortex-induced vibrations of a circular cylinder at different incidence angles

The effects of four different incidence angles (α) on the vortex-induced vibration (VIV) response of a two degrees-of-freedom cylinder were studied using the two-dimensional unsteady Reynolds-averaged Navier-Stokes equation and shear stress transport k-ω model, combined with the fourth-order Runge-Kutta method. The VIV characteristics, including the structural vibration amplitude, vibration frequency, lock-in regime, the pattern of vortex shedding, Strouhal number, hydrodynamic coefficient, and power conversion efficiency were systematically researched. The numerical results showed that a change of the incidence angle made the VIV response of the cylinder display multifrequency characteristics. As the incidence angle increased, the amplitude in the y direction gradually decreased; comparatively, the amplitude in the x direction gradually increased. The VIV responses for different incidence angles all presented an obvious lock-in phenomenon; however, the width of lock-in region changed slightly with variation of the incidence angle. As the incidence angle increased, the root-mean-square value of the hydrodynamic force coefficient in the y direction and the mean value of the hydrodynamic force coefficient in the x direction both had a decreasing tendency.