Flow-Induced Vibration and Hydrokinetic Power Conversion of Two Staggered Rough Cylinders for 2.5 × 104 < Re < 1.2 × 105

Abstract

Flow-induced vibration (FIV), primarily vortex-induced vibrations (VIV), and galloping have been used effectively to convert hydrokinetic energy to electricity in model-tests and field-tests by the Marine Renewable Energy Laboratory (MRELab) of the University of Michigan. It is known that the response of cylinders with passive turbulence control (PTC) undergoing vortex shedding differs from the oscillation of smooth cylinders in a similar configuration. Additional investigation on the FIV of two elastically mounted circular cylinders in a staggered arrangement with low mass ratio in the TrSL3 flow-regime is required and is contributed by this paper. The two PTC-cylinders were allowed to oscillate in the transverse direction to the oncoming fluid flow in a recirculating water channel. The cylinder model with a length of 0.895 m and a diameter of 8.89 cm, a mass ratio of 1.343 was used in the tests. The Reynolds number was in the range of 2.5 × 104 < Re < 1.2 × 105, which is a subset of the TrSL3 flow-regime. The center-to-center longitudinal and transverse spacing distances were T/D = 2.57 and S/D = 1.0, respectively. The spring stiffness values were in the range of 400 < K (N/m) <1200. The values of harnessing damping ratio tested were ζharness = 0.04, 0.12 and 0.24. For the values tested, the experimental results indicate that the response of the upstream cylinder is similar to the single cylinder. The downstream cylinder exhibits more complicated vibrations. In addition, the oscillation system of two cylinders with stiffer spring and higher ζharness could initiate total power harness at a higher flow velocity and obtain more power.