Vortex-induced vibration of a cylinder downstream of an elliptical cylinder with different aspect ratios

The vortex-induced vibration (VIV) of the downstream cylinder of two cylinders in tandem at low Reynolds number of 150 was numerically studied. In all cases, the upstream elliptical cylinder with aspect ratios (AR = 1, 2.3, 2.8, 4, corresponding to an inclined angle of 0 degrees, 30 degrees, 45 degrees, 60 degrees in three-dimensional) was fixed and the downstream cylinder was allowed to freely vibrate in both transverse and streamwise directions. The effects of varying the aspect ratios of the upstream elliptical cylinder on the force coefficients, response amplitude and frequency, motion trajectory, and vortex shedding patterns of the downstream cylinder were studied in detail. The results show that the VIV response is very different from that of an isolated cylinder due to flow interference between the two cylinders. As the aspect ratios increase, the upstream elliptical cylinder becomes more streamlined, which acts analogous to a flow rectifier. Not only does it shorten the distance between the two cylinders, but also it reduces the turbulence intensity of the wake. For this tandem arrangement, the cylinder response in the streamwise direction is more sensitive to the reduced velocity as compared to that in the transverse direction.