A Hybrid CFD and Semi-analytical Model for Streamwise Fluidelastic Instability of Paraller Triangular Tube Bundles

[Background] Fluidelastic instability (FEI) of heat transfer tube bundles under cross-flow conditions represents a critical safety concern in steam generator design, as it may result in tube wear and rupture. While most existing studies have focused on FEI in the lift direction, relatively limited attention has been given to the drag direction. However, recent findings suggest that drag-induced FEI also poses a substantial risk. [Purpose] This study aims to investigate drag FEI using a hybrid CFD–semi-analytical model and determine its critical velocity threshold. [Methods] A two-dimensional CFD model of a single flexible tube in a rigid parallel-triangular array was developed. Transient simulations under cross-flow were performed to capture flow field evolution. Flow channel images were post-processed to extract time delay and decay functions. These functions were embedded into a semi-analytical time-domain model to analyze fluidelastic response. [Results] This paper employs computational fluid dynamics (CFD) to simulate the flow field around a single flexible tube within a rigid, parallel triangular tube array under lateral flow conditions. Time delay and decay functions within the dynamic channel were extracted through post-processing and integrated into a semi-analytical time-domain model to represent fluid-elastic forces in the drag direction. Utilizing this CFD-semi-analytical hybrid model, a time-domain analysis of drag-direction flow-induced instability in the tube bundle was conducted. The predicting critical velocity threshold showed stronggood agreement with existing literature and experiment. [Conclusions] These findingsOur efforts provide valuable insights for the design of heat transfer tube bundles in steam generators, flow-induced vibration analysis, and fretting wear assessment.