Numerical simulation of the VIV of twin tandem diamond cylinders at low Reynolds numbers

To further reveal vibration interference of a multicylinder system, the vortex-induced vibration of two-degree-of-freedom upstream and downstream diamond cylinders with a center-to-center distance L = 5B (B is characteristic length of cylinders) and a mass ratio of the oscillator fixed at m* = 2 was numerically investigated. The influences of the Reynolds number (Re = 40–200) and the reduced velocity (Ur = 3–12) on the dynamic characteristics were considered. The results show that Re has a remarkable effect on the VIV characteristics of twin cylinders, especially on the downstream cylinder. With increasing Re numbers, the lock-in region for the upstream cylinder remains almost constant, while that of the downstream cylinder increases. Unlike the low Re numbers (Re = 40–80), the trajectory of the upstream cylinder at high Re numbers is a closed ring shape rather than a figure “8” within the lock-in region. The downstream cylinder is dominated by transverse vibration in most cases of Re = 40, while it exhibits a significant vibration in both the streamwise and transverse directions at Re = 80–200. Additionally, the wake of twin cylinders at Re = 40 and Ur = 3–4 displays a steady state. With increasing Re numbers, the steady state disappears, and the wake modes with various reduced velocities at high Re (Re = 120–200) are more complicated and disordered.