Poiseuille flow-induced vibrations of two cylinders in tandem

Laminar flows past two tandem cylinders which are free to move transversely in a parallel-wall channel were studied numerically by the lattice Boltzmann method. With fixed Reynolds number Re=100, blockage ratio,beta=1/4 and structural damping xi=0, the effect of streamwise separation between two cylinders at a range of S/D=[1.1, 10] on the motions of cylinders and fluids was studied for both mass ratios of m*=1 and m*=0.1. A variety of distinct vibration regimes involving periodic, quasi-periodic and non-periodic vibrations with corresponding flow patterns were observed. A detailed analysis of the vibration amplitudes, vibration frequencies and relative equilibrium positions for both mass ratios demonstrated that as S/D increases, the interaction of the two cylinders first enhances and then reduces. In the strong coupling regime, both cylinders oscillate periodically around the centerline of the channel with large vibration amplitudes and high vibration frequencies. By comparing with the case of an isolated cylinder, a further study indicated that the gap flow plays an important role in such a dynamic system, and the vortex cores formation behind the front cylinder causes the interaction of the cylinders decouple rapidly. Based on the present observations, such a dynamic model system can be considered as a novel type of vortex-induced vibrations (VIV) and is expected to find applications in fluid mixing and heat transfer. (C) 2013 Elsevier Ltd. All rights reserved.