Two-phase flow-induced vibrations is a phenomenon that occurs when two-phase gas-liquid flows encounter mechanical systems such as pipes, tubes, or heat exchangers. This dynamic interaction between the fluid flow and the structural components can lead to various types of vibrations, which can have detrimental effects on the integrity and performance of the system. Understanding and mitigating two-phase flow-induced vibration is crucial in ensuring the safe and reliable operation of industrial processes involving multiphase flows. To address the complexities of cross-flow induced vibrations, it is essential to bridge the gap between theoretical models and real-world behaviour. While there have been valuable insights gained from existing experimental campaigns, the intricacies of two-phase cross-flow and tube vibration response require further exploration. Previous studies have provided foundational knowledge, but the dynamic and evolving nature of nuclear technology necessitates continuous research and refinement of our understanding. Therefore, there is a continuous need for new experimental campaigns explicitly designed to dig into the complexities of two-phase cross-flow-induced vibrations. Such campaigns should focus on collecting data that can be used to validate computational fluid dynamics (CFD) models, which are indispensable tools for predicting complex flow patterns and vibration responses in these systems. By synergizing experimental data with advanced CFD simulations, researchers can develop more accurate predictive models and, in turn, enhance the safety, efficiency, and longevity of steam generators and nuclear power plants as a whole. Hence, the objective of the present work is to take a step forward in this direction. The primary aim of this study is to comprehend the fundamental vibration excitation mechanisms occurring in tube bundles under two-phase cross flow. Specifically, the objective is to carry out meticulous measurements of two-phase flow characteristics and tube vibration. In order to accomplish this a new test facility named TREFLE (Two-phase flow REgimes and FLuid-structure interaction Experimental facility) was installed in 2022. One of the purposes of TREFLE is also to gather high quality data CFD-grade for the validation of multiphase CFD simulation tools. Organized into four parts, the manuscript begins by describing the TREFLE facility's design and its design process, which is the result of a literature study and is supported by CFD simulations and finite element analysis. It then proceeds to the experimental characterization of two-phase flow in bubbly and intermittent flow regimes across a tube bundle, along with the analysis of tube vibration response. These experimental campaigns focus particularly on the inlet conditions of the two-phase flow and its development within the tube bundle, revealing interesting findings about how the inlet conditions affect the two-phase flow's development within the bundle. The tube vibration response can be linked to the two-phase flow characteristics, providing valuable insights into how the flow regime can impact vibration characteristics. Finally, the manuscript presents and discusses simulations conducted using the Neptune CFD code based on the aforementioned experimental campaigns. The numerical simulations contribute to the understanding of the physics behind two-phase flow and reveal intriguing findings regarding the effect of boundary conditions.
| Author |
| Giuseppe SPINA |
| Date of presentation |
| 2023, 5 december |
| Keywords |
| Two-phase flow, Flow regime, Flow inducted vibration, CFD, Cross-flow, Tube bundle |
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