Numerical investigation on vortex-induced vibrations of four circular cylinders in a square configuration

This paper presents a numerical study of two-degree-of-freedom vortex-induced vibration of four elastically mounted circular cylinders in a square arrangement at a low Reynolds number of Re = 150 and mass ratio of 2.0. The incident angle alpha is ranged from 0 degrees to 45 degrees and the reduced velocity V-r is ranged from 3 to 14. The effects of incident angle and reduced velocity on the dynamic responses and wake flow patterns behind four cylinders are investigated. The results show that the incident angle has a significant effect on the vibration amplitudes and force coefficients of four cylinders, especially for the downstream cylinders, where the maximum vibration amplitudes and force coefficients are occurred mostly on the downstream cylinder. With increasing of the incident angle alpha, the orbital trajectory for each cylinder becomes irregular and complicated, especially at high reduced velocities V-r >= 8, corresponding to multiple oscillation frequencies. Moreover, the wake flow patterns behind four cylinders are modified significantly with variations of incident angles, accompanied by different vortex shedding modes.