The prediction of fluidelastic forces in triangular tube bundles subjected to a two-phase flow: The effect of the flow approach angle

Abstract 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.