Numerical investigation of vortex-induced vibrations of a rotating cylinder under wake interference at low Reynolds number

Investigating the vortex-induced vibrations (VIVs) of an elastically mounted, rotating cylinder under wake interference is crucial for the vibration suppression design of rotating cylindrical structures in complex environments. This study numerically investigates the transverse VIV of an in-line downstream rotating cylinder under the wake interference of an upstream fixed cylinder at various spacing ratios Lx/D (where Lx and D denote the center-to-center distance and cylinder diameter, respectively), using user-defined functions in Fluent and the overset grid method. The simulation parameters include a mass-damping ratio of 0.014, Reynolds number of 150, reduced velocity Vr [Vr=U/fnD, where U represents the uniform freestream velocity and fn denotes the structural natural frequency] ranging from 2 to 16, and a rotation ratio of 1. The transverse vibrational amplitude under wake interference of a rotating cylinder is characterized by a non-monotonic evolution with the Vr, transitioning through five distinct regimes: initial branch, rapid amplification, upper branch (high-amplitude lock-in), rapid decay, and low branch. Within the upper branch, the rotating cylinder exhibits larger transverse amplitudes than its isolated counterpart. The maximum nondimensional transverse amplitude at Lx/D=3 and Vr=9 is approximately twice that of an isolated rotating cylinder. Moreover, compared to an isolated rotating cylinder, the rotating cylinder under wake interference exhibits a wider lock-in range and smaller mean lift and drag coefficients. Due to wake interference, a drag inversion Lx/D is observed for the rotating cylinder, with simulation results indicating this inversion occurs between Lx/D=3.5 and 4. Spanwise vorticity contour plots reveal that parallel 2S (two single vortices per cycle) vortex and chaotic vortices are the primary causes responsible for the maximum amplitude responses of the rotating cylinder under wake interference.