CFD ANALYSIS OF FLOWING FIELD IN 5×5 ROD BUNDLE WITH MULTI-GRIDS

摘要

To study the characteristics of flowing field in fuel bundle, the 5×5 rod bundle with one spacer grid and two mixing grids has been taken for investigation. Geometry model of the mixing vane grids is simplified to be made of mixing vane, steel convex, spring and stripe. The 3-D flow field and heat transfer have been simulated with the CFD code. Much effort has been made to analyze the effect of different grid type and geometry on flowing field in the bundle channels. Also the turbulent mixing performances of different type of grids have been investigated. What's more, the effect of mixing vane on the flowing field, with change of its deflection angle and spread length, have been investigated. The research shows that the spacer grid in the upstream has stronger effect on the flowing field than spacer grid in the downstream. Both the mixing vane grids and support grids have positive effect on heat transfer enhancement. Geometry of the vanes, the deflection angle and length of mixing vanes, has significant effect on cross flow between the flowing channels, increase the deflection angle and length of mixing vanes will make the lateral mixing stronger, but enhance the pressure drop at the same time.