Fluid-Elastic Instability of U-Tube Bundle in Two-Phase Cross-Flow

The U-bend region of nuclear steam generator tubes which undergoes high flow two-phase flow condition is highly susceptible to flow-induced vibration. In various flow-induced vibration mechanisms, it is generally known that fluid-elastic instability is the main cause of fretting wear of U-tubes. Since 1980s many experiments have been performed to investigate the fluid-elastic instability in two-phase cross-flow. Most of the previous experiments were performed with cantilever tube bundles. However, the vibration mode shapes of U-bend tube are quite different from those of cantilever tube, and moreover vibration of U-bend is excited by non-uniform velocity field. The purpose of the present study is to experimentally investigate the fluid-elastic instability characteristics using U-bend tube bundles under air-water two-phase cross-flow