Effect of harmonic inflow perturbation on the wake vortex dynamics of a cylinder undergoing two-degree-of-freedom vortex-induced vibration near a plane boundary

The influence of inflow perturbations on the wake dynamics and structural response is investigated for a cylinder undergoing vortex-induced vibrations (VIV) in oscillatory flows in the proximity of a solid boundary. Numerical simulations are conducted at a Reynolds number of 200, based on the cylinder diameter and free-stream velocity, for perturbation frequencies fp up to four times the natural shedding frequency fo. Three response regimes are identified: a lock-on regime at fp = 2fo, with maximum cylinder displacement and forces, a force-amplification regime for 1.8 < fp < 2.3 characterized by shedding frequency entrainment and a weakly-coupled regime. The wake and structural response dynamics differ from those for unperturbed VIV in uniform flow. The primary mechanism underlying these differences is due to the symmetric instability of the shear layers forced by the perturbations. This instability results in the shedding of vortex pairs at fp in the cylinder base region, which interact with the Kármán formation process and, inthe amplification regimes, reinforce the natural instability at 2fo. These mechanisms give rise to distinct wake topology, which is then related to the structural dynamics.