Influence of path orientation on rectilinear vortex-induced vibrations at subcritical Reynolds number

A circular cylinder mounted on an elastic support and free to translate along a rectilinear path in a uniform cross-current constitutes a canonical problem for investigating vortex-induced vibrations (VIV), a ubiquitous form of flow-induced vibrations driven by flow-body synchronization. When the direction of motion is normal to the current, previous works have shown that VIV can appear for Reynolds number (Re) values as low as 20 (based on cylinder diameter and inflow velocity), below the critical value of approximately 47, marking the onset of flow unsteadiness for a fixed body. The influence of path orientation on the system behavior has been well documented for Re above the critical value, but it remains unexplored in the subcritical range. This is the focus of the present numerical study, which uncovers the progressive expansion of the subcritical-Re region where VIV occur, along with the amplification of vibrations in this region, as path orientation varies from the streamwise to the normal direction. The study also reveals persistent subcritical-Re features related to vibration onset and force-displacement phasing that are independent of path orientation.