Vortex-induced vibration response of a circular cylinder surrounded with small rods

In this paper, cross-flow vortex-induced vibration (VIV) responses of a circular cylinder surrounded with different control rods have been investigated in a wind tunnel. The number of rods n is set equal to 3 and 6, and the ratios of diameters d / D (where d is the diameter of small rods, D is the cylinder diameter) are assumed to 0.10, 0.16 and 0.20. The spacing ratios of s (s = G / D, where G is the gap distance between the main cylinder surface and the control rod surface) are selected as 0.2, 0.4 and 0.6 respectively. The Reynolds number based on the main cylinder is in the region of Re = 4 000-42 000. Results show that the VIV can be significant suppressed if placing the control rods in appropriate arrangement. And the gap between the rod and the main cylinder plays a more important role in the VIV amplitude response. When the spacing ratio between the rod and main cylinder is 0.2, VIV can be best suppressed by 96.7%. However, rods do not always suppress VIV and the responses can be more severe in other spacing ratios (s = 0.4, 0.6). And typical vortex shedding frequency lock-in phenomenon can be observed. When the spacing ratio is 0.2, other than the natural frequency component, St frequency is also presented in the frequency spectrum of wake velocity.