The effects of spacing and damping on vortex-induced vibration of two rigidly coupled circular cylinders in tandem arrangement

This numerical study examines the effect of spacing (L) ranging from 2.0–6.0 and the damping ratio (ζ) from 0 to 0.30 on flow characteristics and power generation from two rigidly coupled equal-diameter cylinders in tandem undergoing vortex-induced vibration. Two-dimensional simulations are performed over a reduced velocity (U*) range of 3.0–15.0, with a fixed mass ratio m*=2.0 and Reynolds number Re = 150. The maximum vibration amplitude and corresponding U* increase with the increase in L for undamped and damped responses. Average power is observed to be a non-monotonic function of U*. The maximum average power increases with L, reaches a peak at L=5.0, and then decreases with further increase in L. The optimal damping for maximum power is also found to be a non-monotonic function of L. The peak of non-dimensional extracted power is equal to 0.245, which is two times that of a single cylinder at L=5.0. Maximum average power is formulated as an exponential function of mass–damping parameter (α=m*ζ). Power extraction efficiency, defined as the ratio of average extracted power to the available fluid power, peaks at L=5.0. Power density, the ratio of extracted power to the available flow power in a volume occupied by the cylinders, reaches its maximum at L=3.0. Considering both energy output and structural compactness, L=3.0 offers the most cost-effective configuration.