Study on Two-Phase Flow Behavior and Turbulent Excitation Mechanism in a U-Bend Tube-Bundle in Steam Generators Based on Air-Water Two-Phase Flow Model Tests.

Flow fields and tube exciting forces were investigated in straight tube-bundles and in a U-bend tube-bundle for several conditions of air-water two-phase flow. The two-phase turbulent exciting forces were correlated with the local flow behavior to elucidate the excitation mechanism. In the straight tube-bundles, the excitation was found to be due to the impact force of water slugs passing around the tubes, which is proportional to the dynamic pressure of the water slug. The estimation formula thus obtained was applied to the U-bend environment and it agreed fairly well with the measured result. Thus the excitation mechanism and its relation with the local flow field has become clear