This study investigates vortex-induced vibrations (VIV) in tandem cylinders, modeling basic configurations relevant to reactor fuel rods. Utilizing Reynolds-Averaged Navier–Stokes (RANS) equations with the Shear Stress Transport (SST) \(k{-}\omega\) turbulence model, it examines how cylinder spacing ratios ( \(Sx/D = 2, 3, 5, 9\) ) and reduced velocities ( \(Ur = 2\,to\,14\) ) influence vibrational and vortex dynamics. Mesh and timestep sensitivity analyses confirm computational reliability, with discrepancies under 2%, and the vibrational amplitude simulation showed good matching against experimental data from literature. The results highlight distinct behaviors between upstream and downstream cylinders in tandem configurations. At closer spacing, the upstream cylinder shows pronounced vibrations due to strong wake interference, while the downstream cylinder experiences amplified responses influenced by the disturbed flow. As the spacing increases, interference effects diminish, leading to upstream cylinder responses resembling those of a single isolated cylinder. However, downstream vibrations remain significant, reflecting ongoing wake interactions. The study also reveals that vortex shedding patterns transition from irregular and chaotic at closer spacing to more stable and periodic at greater distances. This evolution is shaped by the interaction between flow velocity and the spacing between cylinders. Lift forces acting on the cylinders are strongly influenced by these interactions, with the downstream cylinder generally experiencing larger fluctuations. These findings emphasize the complex dynamics of fluid–structure interactions in tandem cylinder configurations, offering valuable insights for applications like optimizing designs to reduce vibrations and ensure structural stability in engineering systems.