An experimental study on the cross-flow vibration of a flexible cylinder in cylinder arrays

In the experiment, a monitored cylinder equipped with two accelerometers inside was flexibly mounted in a water tunnel, surrounded by one to six identical cylinders elastically mounted in rotated triangular pattern. The amplitude diagrams, spectra and orbits of the cylinder motion are used to examine the vibration behavior of the cylinder under the various test conditions of the free stream velocity, the number of the surrounding cylinders, and the cylinder's natural frequency. In the case of the monitored cylinder having the same natural frequency as the surrounding cylinders (22 Hz), amplitude response shows that fluid elastic instability occurs when the flow velocity is above a critical value for the cylinder in all the six-cylinder arrays. Above the critical velocity, the cylinder vibrates around an oval orbit with line-dominated spectrum, implying that the cylinder behaves like an oscillator with the streamwise and cross-stream responses have the same frequency but with a phase shift. By comparison of amplitude diagrams of the cylinder in the six bundles, it reveals that the upstream cylinders have significant influence on the amplitude response of the monitored cylinder-promote the fluid elastic instability of the monitored cylinder, and enhance the cylinder vibration above the critical velocity. The downstream cylinders could suppress the vibration amplitude while the number of the downstream cylinders has little effect on the amplitude response. In case of the monitored cylinder having different natural frequency from that of the surrounding cylinders, it is found that the difference in natural frequency of the cylinders has little effect on the critical velocity, but strong influence on the vibration amplitude above the critical velocity.