An investigation of flow-induced vibrations (FIV) during cold testing on a helical tube steam generator for a high-temperature gas-cooled reactor (HTGR)

Flow-induced vibration (FIV) is a critical phenomenon where the interaction between flowing fluid and structural elements, such as pipes or tubes, results in vibrations, which may compromise system integrity. This research aims to model and simulate the behavior of a helical tube steam generator designed for High-Temperature Gas Reactors (HTGRs), employing the latest ANSYS software licensed by BRIN. The study addresses the problem of understanding fluid flow on steam generators’ vibration characteristics to improve their stability and reliability. This work analyzes the system’s pressure distribution, mass flow, and vibration frequencies under cold testing and turbulent conditions. The findings of this research lie in its specific focus on identifying risks of flow-induced vibrations under non-thermal conditions, an area that is rarely studied but essential for evaluating mechanical reliability during cold testing scenarios. This approach fosters a deeper understanding of the pure impact of fluid dynamics on tube structures without the complications of thermal phenomena. The one-way FSI method with external load was chosen over system coupling because it directly maps fluid-induced forces to the structural domain without requiring repeated bidirectional convergence. This approach is computationally efficient and has been extensively validated for scenarios where fluid-to-structure interactions dominate. Results indicated a pressure drop from 16 MPa at the inlet to 15.3 MPa at the outlet. Modal analysis revealed a range of natural frequencies from 0.32 Hz to 28.35 Hz. Additionally, the calculated flow-induced shedding frequency was 39.7 Hz, while the natural frequency of the helical tube stood at 16.25 Hz. The Reynolds number (Re) and Dean number (De) were determined to be 48,921 and 50,383, respectively, confirming the presence of turbulent flow. The study highlights the risk of resonance when the natural frequency approaches the shedding frequency, which could lead to excessive vibrations and potential structural damage. These findings provide valuable insights for developing safer and more efficient steam generators.