One of the major considerations in the design and operation of heat exchangers is the flow-induced vibration (FIV). While there are multiple FIV excitation mechanisms, fluidelastic instability (FEI) is by far the most crucial mechanism as it can significantly compromise the structural integrity of the tube arrays. Traditionally, it was assumed that FEI could only happen in the transverse direction. However, recent tube failures in replacement steam generators have demonstrated that FEI can occur in the streamwise direction and be equally devastating. This new phenomenon has sparked intensive research to uncover its nature.

An intensive experimental research program was launched to investigate the geometrical impact of various tube array types on the FEI in both the transverse and streamwise directions. To that end, the stability of a single flexible tube and multiple flexible tubes in tube arrays were tested. The study will focus on the stability behavior of parallel triangular arrays at pitch ratios in the range of 1.25 to 1.7. A comparison between the available experimental data and the current results was presented. The current results reveal 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.

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