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Numerical Prediction of the Streamwise Fluidelastic Instability in Two-Phase Flows
Omar Sadek, Atef Mohany, Marwan Hassan

Last modified: 2018-05-27

Abstract


Fluidelastic instability (FEI) is the most devastating form of flow-induced vibrations in tube bundles. During the past decades, it has been widely accepted that the transverse FEI is the critical direction. As such, if the transverse FEI threshold is not reached would automatically lead to avoiding the dangers of streamwise FEI being excited. Therefore, the majority of the literature’s body focused on the investigating and characterizing the transverse FEI. However, recent failures in newly installed nuclear steam generators were attributed to streamwise FEI. Since then, streamwise FEI has gained more attention as a potential cause of damage to nuclear steam generators. In this work, a numerical model is developed to study and predict the onset of the streamwise FEI. Simulations were conducted for a parallel triangular tube bundle. The model was validated and tested against the available experimental data in the literature for single phase and two-phase air-water mixture flows. Three different geometries with pitch-to-diameter ratios of 1.3, 1.5, and 1.7 are investigated and presented in this study for water and 60% air void fraction flows. The study confirms the strong dependency of the onset of streamwise FEI on the pitch-to-diameter ratio and void fraction.

Keywords


Fluidelastic Instability; Two-phase flow; CFD

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