Investigation of added mass coefficient of helical tube bundles in steam generator based on finite element modal analysis

The helical coil once-through steam generator (OTSG) is widely used in the design of integrated pressurized water reactors (IPWRs) due to its compact structure and high heat transfer efficiency. During the operation of OTSG, the helical tube is continuously flushed by the coolant. To prevent flow-induced vibrations (FIV), which can lead to tube wear, damage, or even rupture, FIV calibration is essential throughout the design process. The added mass coefficient, a key parameter in calibration, is closely linked to the prediction of natural frequency and directly impacts the risk assessment of FIV. Therefore, a more comprehensive and in-depth study of the added mass coefficients of helical tube bundles is crucial for the structural optimization and safety analysis of OTSGs. This study investigates the effects of structural parameters, such as pitch ratios and tube bundle arrangements, on the natural vibration characteristics and added mass coefficients of helical tube bundles coiled in the same direction within a liquid environment. Large-scale modal analyses using finite element methods are conducted to explore the trend of the added mass coefficient as a function of varying structural parameters. The results are compared with those of tube bundles coiled in the opposite direction to examine the differences between various coiling configurations. A unified set of recommended curves for the added mass coefficients is proposed to assist engineers in efficiently determining the natural frequency of helical tube bundles with varying pitch ratios in the fluid and avoiding resonance failure. The research outcomes are fundamental to improving FIV analysis methods of helical tube bundles and enhancing the structural integrity of OTSGs.