Numerical simulation of vortex-induced vibration of two long flexible circular cylinders in tandem

A quasi three-dimensional numerical model is developed to study vortex-induced vibration (VIV) of two tandem flexible circular cylinders. In this model, the whole cylinder is divided into many sections along its length. The hydrodynamics of each section are represented by the solution of the two-dimensional Navier-Stokes equations. The dynamic response of the flexible cylinder is predicted by the solution of the three-dimensional equations of motion of a tensioned vertical cylinder. Simulations of two identical cylinders are carried out with a same mass ratio of 2.453 and a large aspect ratio of 3691. The centre-to-centre distance between two tandem cylinders is 5D. A low Reynolds number of 200 is used in the simulations, and the reduced velocity based on the fundamental natural frequency is 32.1. The numerical results show that the sixth mode vibration is excited on the upstream cylinder and its dynamic response is very similar to that of the isolated cylinder. However, due to the effect of wake interference, the response of the downstream cylinder is quite different from that of the upstream cylinder. It is mainly controlled by the third order mode although multi-mode vibration is involved. The highly irregular vortex shedding pattern of the downstream cylinder is distinct to the regular 2S vortex shedding mode of the upstream cylinder.