Study On 3-D Flow Field Of Rod Bundles With Spacer Grids

This paper calculated and analyzed 3-D single-phase flow field of rod bundles with spacer grids by numerical method in order to validate the applicability of numerical method and find out the influence of spacer grids to flow field in rod bundles.Sensitivity analyze had been carried out in accordance with different calculating conditions, and found out some fitted numerical methods in analyzing the fluid field of rod bundles with spacer grids, mainly the following aspects:1. Changed the line contact to surface contact between the spring, dimple and fuel rods;2. Used hybrid mesh technology to generate the computation grids in the computed domain;3. Selected the SST k-ωturbulence model to compute this problem;4. Specified Blend Factor (β= 0.5) advection scheme was adopted;5. Set the entrance length to 300mm can satisfy the computation demand.In order to verify the correctness of the computed results, this paper had compared the measured data with the computed value. The results indicated that the calculated and measured lateral velocity were close to zero before passing the spacer grid; after passing the spacer grid, intense lateral velocity was found close to the spacer grids (about 5 times equivalent diameter), measured and computed value distributed with parabola law, and both agree well; measured and computed lateral velocity attenuated obviously downstream of the spacer grids (about 32 times equivalent diameter), both of them were close to zero and agree well; The distributing tendency of computed and measured axial velocity agree well; downstream of the spacer grids (about 5 times equivalent diameter) the deviation of axial velocity was larger, but below 20%, other cross section below 7.5%. Calculated drag coefficient perfectly accordant with the measured value except the friction coefficient of little Reynolds number where derivation achieve 15%.These analyses indicated that this numerical computation was very successful; it laid the foundation of optimal design of spacer grids.The calculation of different structure of spacer grid indicated that the mixing vane was the main reason of cross flow; spring and dimple influenced the axial velocity obviously, specially the spring, whose incident face was large, and hence caused axial velocity fluctuate largely because of its strong block effect; the mixing vane can blending and averaging the axial velocity; spring and dimple influent the drag coefficient obviously, the results of calculation indicated that the drag coefficient of spring and dimple was 1.5 times of mixing vane, these indicated that spring and dimple cannot be neglected in thermal-hydraulic design.