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 dam** 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 dam** 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 dam**, 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 dam**. This value is close to that of an isolated circular cylinder. The vibration amplitude decreases with increasing dam** 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 dam**. The mean extracted power is maximized at certainly reduced velocities in the synchronization region at each dam** value. The extracted power is proportional to both dam** and vibration amplitude. Since the vibration amplitude reduces with dam**, an optimal dam** 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.