물-공기 횡류시 U 자형 튜브 다발에서의 유체탄성불안정

In the present study, a series of experiments have been performed to investigate a fluid-elastic instability of an U-tube bundle in air-water two-phase cross-flow. A total of 39 prototypic U-bend tubes are arranged in a rotated square array with a p/d of 1.633, which is identical to U-bend tube bundle of OPR1000 steam generators. The present experimental facility has 2-span U-tubes in contrast to 9-span U-tubes of OPR1000 steam generators. However, modal analysis shows that the major vibration mode and corresponding natural frequencies are almost same to the full 9-span U-tubes. A total of 12 3-axis acceleromters are installed inside U-tubes to monitor a precise vibration motions. The following parameters were obtained throughout a series of experiments: tube vibration responses and critical velocity for fluid-elastic instability, two-phase damping ratio, hydrodynamic mass. Finally, the instability factor (K) of Connors’ relation was evaluated based on the above measured parameters.