Stability behaviour of a rotated square tube array subjected to two-phase cross-flow

• Published in: Nuclear engineering and design 2023-05, Vol.406, p.112235, Article 112235
• Main Authors: Darwish, Sameh, Mureithi, Njuki, Cho, Minki
• Format: Article
• Language: English
• Subjects: Fluidelastic instability; Quasi-steady model; Rotated square array; Steam generator; Two-phase flow
• ISSN: 0029-5493; 1872-759X
• DOI: 10.1016/j.nucengdes.2023.112235

Theoretical analysis of fluidelastic instability of tube arrays operating in two-phase flow, in particular, for rotated square arrays, remains limited. In this paper, an experimental programme was carried out to gain insight into the rotated square array fluidelastic forces. The quasi-steady model is used to predict the fluidelastic behaviour of a rotated square array having pitch spacing ratio P/D = 1.64. A test apparatus is designed to measure the quasi-static fluid forces in single phase (water) and two-phase (air–water) flow for a wide range of void fractions. Both streamwise and transverse directions are considered in the study by measuring the forces and their derivatives with respect to tube finite displacement in both the lift and drag directions. The cross coupling fluid forces are incorporated into the quasi-steady model to investigate the existence of the stiffness-controlled instability mechanism in this array. The results of the theoretical analysis were compared with fluidelastic instability experimental data for the same array. Agreement between the theoretical results and the experiment is shown to be good. In general, the stable behaviour of this array in two-phase flow was confirmed. The analysis showed the vulnerability of this array to transverse fluidelastic instability in water flow in the case of the fully flexible array. This analysis is also used to investigate the array behaviour in the 97% void fraction and results are compared with those exported experimentally. Compared to the lower void fractions, the damping is, uniquely in the 97%, invariably behaving with the flow velocity increase. This is relatively consistent with the observed fluidelastic instability from the experiments. •Measuring, for the first time, the quasi-static fluid forces of a rotated square array.•Measurements were performed in the streamwise and transverse directions.•Integrating the measured force coefficients into a quasi-steady model.•Analysing the fluidelastic behaviour of the array.•Transverse fluidelastic instability occurs in water flow when multiple flexible tubes are used.•Stablility of the rotated square array in two-phase flow is confirmed.•Stable behavior is a result of the fluid damping increase with flow velocity.