This study investigates the influence of a free end on flow-induced vibration (FIV) and energy harvesting from Passive Turbulence Control (PTC) cylinders through three-dimensional numerical simulations. Specifically, the research focuses on PTC cylinders with a length-to-diameter ratio (L/D) of 3.14, comparing their vibration response and energy harvesting capabilities against infinitely long cylinders that lack a free end. The analysis demonstrates that the presence of a free end significantly modifies the wake dynamics and fluid-structure interactions involved, resulting in a higher flow speed threshold necessary to initiate FIV, as well as an increase in vibration amplitude. Although cylinders with free ends require greater flow speeds to begin energy collection, they ultimately exhibit a higher power output, albeit at a lower efficiency compared to their infinitely long counterparts. Furthermore, a comprehensive investigation is conducted on cylinders with varying length-to-diameter ratios (L/D = 1, 3.14, and 10), revealing that the influence of the free end diminishes as the length of the cylinder increases, with the shorter cylinder demonstrating the most pronounced effects. This research provides valuable insights into optimizing the design and application of PTC cylinders for energy harvesting in turbulent flow conditions.