Research on In-plane Fluid-elastic Instability of Heat Transfer Tube in Steam Generator

Due to a small gap between the anti-vibration bars (AVBs) and the heat transfer tubes, and according to the position of AVBs and the number of continuous failures of the in-plane support, the in-plane restraint failure analysis of AVB is divided into 13 cases. The influence of the restraint failure on the in-plane mode of the heat transfer tube under different cases is analysed. The mode damping ratio was calculated by performing a weighted average method based on the mode shape function, and then the effects of different restraints by AVBs on fluid-elastic instability of steam generator tubes are studied. The analysis results show that with the increase of the continuous failure position of the in-plane support, the first-order modal frequency in the elbow zone decreases continuously, and the mode shape appearing in the elbow zone becomes more obvious. The first-order mode in the elbow zone is not necessarily the mode in which the largest fluid-elastic instability ratio occurs. The vibration mode with the largest ratio of the fluid-elastic instability appears almost in the elbow zone. With the increase of the continuous failure position of the in-plane support, the fluid-elastic instability ratio increases continuously. When three or more continuous AVBs fail in-plane, fluid-elastic instability will occur.