The U-bend region in a typical steam generator is characterized by two-phase flow conditions and susceptible to damage due to fluidelastic instability excitation. To prevent such a destructive fluid–structure mechanism, numerous experimental and numerical works have been done to investigate, understand, and devise techniques to mitigate it. The effect of the flow approach angle on fluidelastic instability remains one of the topics which has not been fully resolved. This work aims to utilize flow numerical modeling techniques to gain an understanding of such an effect in a two-phase air–water flow. Various flow approach angles ranging from normal to parallel triangular arrays were investigated for various void fractions ranging from water to air flows. The results obtained revealed that the effect of a homogeneous air void fraction is very critical at very high values (99% and above). Moreover, at any intermediate flow approach angle between a normal and a parallel triangular array, the flow inside the array carries features of both normal and parallel triangular flow patterns. Based on this, a new FEI force-approach angle, semi analytical model is proposed to calculate the fluidelastic forces at any flow approach angle. The data obtained from this model were validated against information extracted from flow simulations and showed a good agreement.

典型蒸汽发生器中的 U 形弯曲区域的特点是两相流动条件，并且容易因流体弹性不稳定激励而受到损坏。为了防止这种破坏性的流体结构机制，已经进行了大量的实验和数值工作来研究、理解和设计减轻它的技术。流动接近角对流体弹性不稳定性的影响仍然是尚未完全解决的主题之一。这项工作旨在利用流动数值建模技术来了解空气-水两相流中的这种效应。对于从水流到空气流的各种空隙率，研究了从法线到平行三角形阵列的各种流动接近角。获得的结果表明，在非常高的值（99% 及以上）下，均匀空气空隙率的影响非常关键。此外，在法线和平行三角形阵列之间的任何中间流动接近角处，阵列内部的流动都具有法向和平行三角形流动模式的特征。在此基础上，提出了一种新的FEI力接近角半解析模型来计算任何流动接近角下的流体弹性力。从该模型获得的数据根据​​从流动模拟中提取的信息进行了验证，并显示出良好的一致性。提出了一种新的 FEI 力接近角、半解析模型来计算任何流动接近角下的流体弹性力。从该模型获得的数据根据​​从流动模拟中提取的信息进行了验证，并显示出良好的一致性。提出了一种新的 FEI 力接近角、半解析模型来计算任何流动接近角下的流体弹性力。从该模型获得的数据根据​​从流动模拟中提取的信息进行了验证，并显示出良好的一致性。