Vortex-induced vibration of two rigidly coupled tandem square cylinders at a low Reynolds number

Vortex-induced vibration of two rigidly coupled tandem square cylinders with center spacing L = 4B was numerically investigated at a Reynolds number of Re = 150. Both 2 degrees of freedom (DOF)-C (translational vibration) and 3DOF-C (translational and rotational vibration) cases are considered and compared with the case of no rigid connection. The results reveal that the onset of the synchronization region for rigidly coupled cylinders is earlier than that without connection. Compared with the latter, the upstream cylinder with rigid connection displays a lower transverse amplitude within the synchronization region and a higher one outside the region. The transverse amplitude of the downstream cylinder with 2DOF-C is generally lower than that without connection. In contrast, the vibration of the downstream cylinder with 3DOF-C is higher than that without connection, except for the high reduced velocity, in which the maximum transverse amplitude increases by 20%. The synchronization region of the twin uncoupled cylinders appears within the reattachment and co-shedding regimes, while that of the twin coupled cylinders only appears within the co-shedding regime. Although the synchronization region with a similar flow pattern appears within the co-shedding regime in these three cases, it shows different vibration characteristics.