Flow-induced vibrations occur in general heat exchangers and nuclear reactors. They cause the tube failures through fretting wear or fatigue. Fluid elastic instability may lead to vibration amplitudes large enough to cause tube-to-tube clashing and in such cases will lead to relatively rapid failures. Therefore mechanisms of elastic vibration induced by cross flow are significant problems for large vibration amplitudes. The aims of this study are to analyze the vibration of cylinders at various flow velocities and to get the fundamental data of design for the prevention of accidents in heat exchanger. In this study, the experimental apparatus was built so that cylinder tip motions could be measured at various flow velocities. The experiments were conducted in different cylinder arrays. The cylinder vibration was induced in normal direction to flow by an alternate vortex. Moreover, once the flow velocity was increased to a certain value, the cylinder oscillation amplitude increased rapidly with flow and had a maximum. When five cylinders were arranged in a row normal to flow, the wandering of energy was generated between the two cylinders. For three cylinders arranged in tandem, two cylinders in upstream and downstream positions mutually vibrated out of phase. For many cylinders, the entropy had the maximum at a specific flow velocity and oscillating behavior of cylinders became chaotic state which could not predict its behavior.
