Power Harvesting from VIV of Rigidly-Coupled Cylinders in Tandem Arrangement

Abstract

Power harvesting from vortex-induced vibration (VIV) is a fairly new regime that needs to be explored. A practical VIV-based hydroelectric farm will employ a number of devices undergoing VIV. The present work aims to quantify the energy extraction capability of two rigidly-coupled circular cylinders of equal diameter (D) in tandem arrangement. The energy extraction process is modeled using a damper attached to the vibrating cylinders. The cases with different damping ratios (ζ) are numerically simulated by OpenFOAM, an Open-source software computational fluid dynamics solver. The cylinders are rigidly -coupled and oscillate rigidly in the cross-flow direction. All the cases were simulated at a constant mass ratio, defined as the ratio between net oscillating mass to the mass of displaced fluid, 2 and Reynolds number 150. The gap ratio (L/D), defined as the normalized center-to-center distance between the cylinders in cross-flow direction, is taken as 2. The damping ratio is varied in the range of ζ = 0.025–0.10, and the reduced velocity (U∗) is varied from 3 to 8.5. At the smallest damping, the cylinders vibrate with significant amplitude in the reduced velocity range of 4–6, the synchronization region. A maximum vibration amplitude (y/D) value of 0.51 is observed close to reduced velocity 5 at the smallest damping. This value is close to that of an isolated circular cylinder. The vibration amplitude decreases with increasing damping as some of its kinetic energy is dissipated, which is assumed to equal the extracted power in the present case. The width of the synchronization region also decreases with increasing damping. The mean extracted power is maximized at certainly reduced velocities in the synchronization region at each damping value. The extracted power is proportional to both damping and vibration amplitude. Since the vibration amplitude reduces with damping, an optimal damping value at which a peak value of the maximum extracted power is obtained. For the present case, the non-dimensional peak extracted power is close to 0.069 at ζ = 0.04 and U∗ ≈ 4.5.