Geometrical Effect of Tube Array on Prediction of Fluidelastic Instability – Single Phase Air Flow

Abstract Flow-induced vibrations (FIV) are a major consideration in the design of shell and tube heat exchangers. Among the FIV excitation mechanisms, fluidelastic instability (FEI) is by far the most important mechanism that can significantly compromise the structural integrity of tube arrays. Traditionally, FEI was thought to only occur in the transverse direction. The recent tube failures of replacement steam generators showed that FEI could occur in the streamwise direction and be equally devastating. This has sparked intensive efforts to uncover the nature of this new phenomenon. The current work presents an experimental investigation program which was initiated to systematically uncover fundamental aspects of this phenomenon. Experiments were carried out in an airflow wind tunnel at the University of Guelph in the Fluid-Structure Interaction Laboratory. The aim of this study was to investigate the geometrical effect of tube array types on the FEI in both the transverse and streamwise directions. The stability of a single flexible tube and multiple flexible tubes in tube arrays were tested. Parallel triangle and normal triangle arrays were tested at pitch ratios in the range of 1.25 to 1.7. A compression between the available experimental data and the current result was presented and conclusions were drawn. The results show that the stability threshold is sensitive to the pitch-to-diameter ratio of the array and the number of flexible tubes especially in the streamwise direction.