Investigation of fluidelastic instability in rotated square tube arrays subjected to air flow

Fluidelastic instability (FEI) in steam generators has continued to be a major concern over the last decades, particularly following the unexpected event at the San Onofre Nuclear Generating Station (SONGS). This event resulted in notable tube failures caused by large vibrations amplitudes induced by FEI in the streamwise direction. Despite extensive experimental and numerical efforts to understand the dynamics of tube arrays subjected to cross flow, there is still substantial work required to grasp the factors that influence the onset of FEI in various tube arrangements, particularly in the streamwise direction. This paper provides a systematic investigation of the impact of the array geometry (effect of the array size, array type, pitch ratio and array flexibility level) on the onset of instability for both the transverse and the streamwise directions. A series of wind tunnel experiments were conducted on a rotated square array subjected to air cross-flow with four different pitch ratios. A comparison between the current findings and the accessible experimental data in the open literature was presented. The current research indicates that the pitch ratio of the array, the number of flexible tubes, and the size have a significant impact on the stability threshold in both directions. The results also show that the rotated square array is susceptible to streamwise fluidelastic instability.