A numerical study of vortex-induced vibration (VIV) of two circular cylinders of different diameters in steady flow is carried out. The Reynolds-averaged Navier-Stokes equations are solved using a finite element method (FEM) with a k-ω turbulence closure. The numerical model is firstly validated against VIV of a single circular cylinder in steady flow. Then this model is employed to simulate the flow around two circular cylinders which are mounted elastically. The response amplitude, vibration frequency of the two cylinders and vortex shedding modes are analyzed. It's found that the fluid flow fields and the response behavior are more complex than those of an isolated cylinder. The gap distance and arrangement of the two cylinders affects the VIV significantly.


Extensive research work has been done on vortex-induced vibration (VIV) of an elastically mounted rigid cylinder with low mass-damping coefficient (restrained to move in cross-flow direction). Comprehensive reviews of work done so far can be found in Williamson and Govardhan (2004) and Sarpkaya (2004). VIV of an elastically mounted cylinder is governed by a number of parameters, including mass ratio (m*= (oscillatory mass)/(displaced fluid mass)), damping coefficient ζ, and the reduced velocity (Ur = U / fnD, where U is incoming flow velocity, is the natural frequency of the cylinder and D is the diameter of the cylinder).

Three distinct branches (initial, upper and lower branch) of response were found corresponding to different values of reduced velocity ((Khalak and Williamson, 1996; Khalak and Williamson, 1999) for low mass-damping coefficients (m*ζ), while only two brunches (initial and lower) were found for high mass-damping coefficients (Feng 1968). The so-called "2S" vortex shedding pattern was found in initial branch ("2S" means two single vortices shed in each vibration), and "2P" vortex shedding regime was found in both upper and lower branch.

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