Analysis of Turbulent Structures Based on Large Eddy Simulation in Rod Bundle Channels with mixing vanes

The refinement of thermal-hydraulic calculations for reactors is crucial for both the economy and safety of reactors. However, the spacer grids and mixing vanes will affect the turbulence and vortices. In particular, the prediction of near-wall turbulence using computational fluid dynamics (CFD) is more difficult due to the strong shear stress and anisotropic properties near the coolant channel walls. By studying the turbulent coherent structures in the core coolant channel, it is possible to better predict the turbulent flow and obtain more accurate core thermal-hydraulic parameters. This paper focuses on the experimental objects of AFA-2G spacer grids and mixing vanes and establishes a model that meets the requirements of Large Eddy Simulation (LES) to study turbulent structures. The parameters of the flow field acquired from LES were in good agreement with the experimental results. By comparing with the Reynolds time-averaged model, it was found that its mean field is more accurate. This paper quantitatively analyzed the anisotropic characteristics of coherent structures and visualizes their spatial distribution using barycentric map. The visualization of vortices was performed using Omega criterion, and the dynamic analysis of vortices was conducted to investigate the effects of spacer girds and mixing vanes on the generation and evolution of vortices, as well as their mutual interactions.