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-offreedom 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.

Automated summary

The numerical study reveals that the Reynolds number and reduced velocity have significant effects on the VIV characteristics of twin cylinders, particularly on the downstream cylinder. At high Reynolds numbers, the lock-in region of the downstream cylinder increases, and its trajectory shape becomes a closed ring within the lock-in region. As Reynolds number increases, the downstream cylinder exhibits significant vibration in both the streamwise and transverse directions.