Low drag solutions for suppressing vortex-induced vibration of circular cylinders

Measurements are presented of response and drag for a flexibly mounted circular cylinder with low mass and damping. In one set of experiments it is free to respond in only the cross-flow direction and in a second it is free to respond in two degrees of freedom. It is shown how vortex-induced vibration can be practically eliminated by using free-to-rotate, two-dimensional control plates. Further it is shown that these devices achieve VIV suppression with drag reduction. The device producing the largest drag reduction was found to have a drag coefficient equal to about 60 % of that for a plain, fixed cylinder over the Reynolds number range of the experiments, up to 30 000. The importance of torsional resistance of the devices is discussed and it is shown that if it is too low large oscillations of the device and cylinder will develop and if it is too high galloping is initiated.