Hongwu Zhao

Cylindrical structures are widely used in offshore and marine engineering, but they may suffer from vortex-induced vibration under the influence of ocean or wave currents, which can lead to severe fatigue damage. In this study, we applied the open-source software Open-Source Field Operation and Manipulation (OpenFOAM) to investigate the characteristics of fluid flow around offshore cylindrical structures, taking into account the effect of helical strake parameters, such as pitch and strake number. The aim of this study is to explore the possibility of suppressing vortex shedding with different helical strake parameters. Numerical simulation results demonstrated that attaching a helical strake to the bare cylinder destroyed vortex shedding in offshore cylindrical structures. The vortex visualization showed that the helical strake destroyed the three-dimensional vortex structures. Moreover, the lift coefficient data showed that the vibration frequency of the cylinder decreased after attaching the helical strake, indicating that the vortex-induced vibrations on the wake flow tended to fade. The results suggest that the helical strake is a promising option for suppressing the wake vortex shedding of cylindrical structures in offshore engineering.

The steam generator in a nuclear power plant should provide high quality steam to the turbine for better efficiency and stability. For this purpose, a steam separator is installed in the steam generator to manage the quality of the steam. In this study, computational fluid dynamics (CFD) technique was carried out to analyze the flow phenomenon of the swirl-vane type steam separator. When the steam enters the swirl-vane separator with droplets, it is affected by the centrifugal force. Some of the droplets are attached to the riser wall, some pass through the outlet (bypass and the downstream pipe) and the remaining droplets enter the next separator. A Lagrangian particle model was used to simulate the behaviors of steam and water droplets. The results show that the removal of the droplets depend on the size of the droplets. When the droplet size is small, it is removed by the outlet. In particular for the droplet size of 0.01 micron, over 75% of them are removed. When the droplet size is large, it is collected on the wall. In particular for the droplet size of 50 micron, over 95% of them are collected on the wall. Thus, the performance of the separator decreases as the droplet enters the next separator directly before being collected on the walls or on the outlet if the length of the riser above the swirl-vane is short.