Numerical simulation of vortex induced vibration of three cylinders in regular triangle arrangement

This paper presents a two-dimensional simulation of the vortex induced vibrations of three elastic cylinders in regular triangle arrangement at low Reynolds number. The motion of every single cylinder, which is free to oscillate in two degrees-of-freedom in a uniform flow and has the same mass and natural frequency in both X and Y directions, is modeled by a mass-spring-damping system. The displacement, mean and fluctuating aerodynamic forces, Strouhal number ( St ) and vortex shedding pattern in the wake for each cylinder are analyzed with eight spacing ratios L/D changing from 1.5 to 6.0. The results indicate that the mean drag forces of upstream cylinders are larger than that of downstream cylinder, and the downstream cylinder is usually undergone serious fluctuating lift and drag forces. It is found that the simultaneous resonance in the x- and ydirections may occur for the downstream cylinder and the frequencies of the streamwise and transverse responses are same but with a phase shift. The streamwise oscillation of downstream cylinder could be as large as 1.0D, and the maximum transverse amplitude of three cylinders can reach to 0.85D. It is indicated that the cross-flow oscillation amplitude of three cylinders significantly increased compared with the flow-induced vibration of a single elastic cylinder and the streamwise oscillation of downstream cylinder is unneglectable for vortex-induced vibration of multi-cylinder system.