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.

[背景] 横流工况下换热管群的流体弹性失稳（Fluidelastic Instability, FEI）是蒸汽发生器设计中的关键安全隐患，其可能引发管材磨损与破裂。尽管现有多数研究均聚焦于升力方向的FEI，针对拖曳方向的相关探讨却相对匮乏。但最新研究表明，由拖曳力引发的FEI同样存在显著安全风险。
[目的] 本研究旨在借助混合计算流体动力学（Computational Fluid Dynamics, CFD）-半解析模型开展拖曳方向FEI的相关研究，并确定其临界速度阈值。
[方法] 本研究构建了刚性平行三角排布中单根柔性换热管的二维CFD模型。开展横流工况下的瞬态模拟，以捕捉流场演化过程。对流道图像进行后处理，提取时延函数与衰减函数。将上述函数嵌入半解析时域模型，进而开展流体弹性响应分析。
[结果] 本文采用计算流体动力学（CFD）模拟了横向流工况下，刚性平行三角排布管群中单根柔性换热管周围的流场。通过后处理提取动态流道内的时延函数与衰减函数，并将其集成至半解析时域模型，以表征拖曳方向的流体力弹性作用力。借助该CFD-半解析混合模型，本研究开展了管群拖曳方向流致失稳的时域分析。所得预测临界速度阈值与现有文献及实验数据吻合度极佳。
[结论] 本研究成果可为蒸汽发生器换热管群设计、流致振动分析以及微动磨损评估提供重要参考依据。