加裝在定位格架上的攪混翼具有引導冷卻劑產生橫向流動，改善棒束表面換熱，增加DNB裕量，提高CHF的作用，攪混翼的設計對反應堆堆芯安全有重要的影響。CFD模擬是一種具有安全、成本低及研究週期短等優勢的設計工具，利用CFD模擬探究燃料元件內攪混翼對流動換熱特性的影響具有很高的工程價值。
本文首先通過已有實驗數據進行CFD方法的驗證，確認數值模擬的有效性。同時分別採用標準k-ε模型、SST k-ω模型和雷諾應力模型進行計算，通過對比軸向流速、徑向流速及周向Nu數分佈，分析選出合適的湍流模型，用於後續攪混翼結構參數優化的研究中。
在此基礎上對帶單跨定位格架5×5棒束模型進行數值模擬，分析探究攪混翼偏折角、間距及長度的改變對流動與換熱的影響，以期為未來定位格架及攪混翼的設計提供參考。

The mixing vane installed on the spacer grid of the PWR fuel assembly plays the role of guiding the coolant to generate lateral flow, improving the heat transfer of the rod bundle surface, increasing the DNB margin and increasing CHF. The design of the mixing vane has important influence on the safety of the nuclear reactor core. CFD simulation is a design tool with advantages of safety, low cost and short research period. It is of great engineering value to use CFD simulation to study the influence of mixing vane on the flow and heat transfer characteristics in the fuel assembly.
The CFD method was validated by the existing experimental data. The standard k-ε model, SST k-ω model and Reynolds stress model were employed to confirmed the validity of the CFD simulation. By comparing the axial velocity, lateral velocity and azimuthal Nu number distribution, an appropriate turbulence model was selected for subsequent research on influence of the structure parameters of the mixing vane.
The CFD simulation of the 5×5 bundle model with single-span spacer grid was carried out. The influence of the bending angle, the spacing and the length of the mixing vane on the flow and heat transfer was analyzed in order to provides a reference to the optimization of the mixing vane in the future.

1.Wu X, Trupp A C, “Experimental study on the unusual turbulence intensity distributions in rod-to-wall gap regions”, Experimental Thermal and Fluid Science, vol.6, pp. 360-370,1993.
2.McClusky H L, Holloway M V, Conover T A, et al, “Mapping of the lateral flow field in typical subchannels of a support grid with vanes”, Journal of Fluids Engineering, vol.125, pp. 987-996, 2003.
3.Holloway M V, McClusky H L, Beasley D E, et al, “The effect of support grid features on local, single-phase heat transfer measurements in rod bundles”, Heat Transfer Summer Conference, American Society of Mechanical Engineers, USA, 2003, pp:547-560.
4.Holloway M V, Conover T A, McClusky H L, et al, “The effect of support grid design on azimuthal variation in heat transfer coefficient for rod bundles”, Journal of Heat Transfer, vol.127, pp: 598-605, 2005.
5.Cosby M C, “Effects of support grid vane angles on single phase heat transfer within rod bundle subchannels”, Clemson University, Master Thesis, 2007.
6. Karouta Z, GU C Y, Schoelin B, “3-D flow analyses for design of nuclear fuel spacer”, Proceedings of the 7th International Meeting on Nuclear Reactor Thermal-Hydraulics, USA,1995, pp: 3153-3174.
7.Lee K B, Jang H C, “A numerical prediction on the turbulent flow in closely spaced bare rod arrays by a nonlinear k− ϵ model”, Nuclear Engineering and Design, vol. 172, pp: 351-357, 1997.
8.In W K, Shin C H, Oh D S, et al, “Numerical analysis of the turbulent flow and heat transfer in a heated rod bundle”, Nuclear Engineering and Technology, vol. 36, pp: 153-164, 2004.
9.Holloway M V, Beasley D E, Conner M E, “Investigation of swirling flow in rod bundle subchannels using computational fluid dynamics”,14th International Conference on Nuclear Engineering, American Society of Mechanical Engineers, USA, 2006, pp: 1-11.
10.Liu C C, Ferng Y M, Shih C K, “CFD evaluation of turbulence models for flow simulation of the fuel rod bundle with a spacer assembly”, Applied Thermal Engineering, vol.40, pp: 389-396, 2012.
11.Jin H, Lee Y, Park N, “CFD analysis on a three by three nuclear fuel bundle with five spacer grid assemblies”, Journal of Mechanical Science and Technology, vol.26, pp:3965-3972, 2012.
12.Podila K, Rao Y, “CFD modelling of turbulent flows through 5× 5 fuel rod bundles with spacer-grids”, Annals of Nuclear Energy, vol.97, pp: 86-95, 2016.
13.Chen X, Du S, Zhang Y, et al, “Validation of CFD analysis for rod bundle flow test with vaned spacer grids”, Annals of Nuclear Energy, vol.109, pp: 370-379, 2017.
14.Mikuž B, Tiselj I, “URANS prediction of flow fluctuations in rod bundle with split-type spacer grid”, International Journal of Heat and Fluid Flow, vol.64, pp: 10-22, 2017.
15.Chen G, Zhang Z, Tian Z, et al, “Design of a CFD scheme using multiple RANS models for PWR”, Annals of Nuclear Energy, vol.102, pp: 349-358, 2017.
16.Xiang-Zhe CUI, Kwang-Yong KIM, “Three-Dimensional Analysis of Turbulent Heat Transfer and Flow through Mixing Vane in A Subchannel of Nuclear Reactor”, Journal of Nuclear Science and Technology, vol.40, pp:719-724, 2003.
17.Kim K Y, Seo J W, “Shape optimization of a mixing vane in subchannel of nuclear reactor”, Journal of Nuclear Science and Technology, vol.41, pp: 641-644, 2004.
18.Ikeda K, Makino Y, Hoshi M, “Single-phase CFD applicability for estimating fluid Hot-Streak locations in a 5× 5 fuel rod bundle”, Nuclear Engineering and Design, vol.236, pp: 1149-1154, 2006.
19.Ikeda K, “CFD application to advanced design for high efficiency spacer grid”, Nuclear Engineering and Design, vol.279, pp: 73-82, 2014.
20.Lee C M, An J S, Choi Y D, “Thermo-hydraulic characteristics of hybrid mixing vanes in a 17× 17 nuclear rod bundle”, Journal of Mechanical Science and Technology, vol. 21, pp: 1263-1270, 2007.
21.Nematollahi M R, Nazifi M, “Enhancement of heat transfer in a typical pressurized water reactor by different mixing vanes on spacer grids”, Energy Conversion and Management, vol.49, pp:1981-1988, 2008.
22.Navarro M A, Santos A A C, “Numerical evaluation of flow through a 5x5 PWR rod bundle: effect of the vane arrangement in a spacer grid”, International Nuclear Atlantic Conference, Brazil, 2009
23.Seo, Han, et al, “Swirling performance of flow-driven rotating mixing vane toward critical heat flux enhancement”, International Journal of Heat and Mass Transfer, vol.89, pp: 1216-1229, 2015.
24.In W K, Oh D S, Chun T H, “Flow analysis for optimum design of mixing vane in a PWR fuel assembly”, Nuclear Engineering and Technology, vol.33, pp: 327-338, 2001.
25.In W K, Chun T H, Shin C H, et al, “Numerical computation of heat transfer enhancement of a PWR rod bundle with mixing vane spacers”, Nuclear Technology, vol.161, pp: 69-79, 2008.
26.Liu C C, Ferng Y M, “Numerically simulating the thermal–hydraulic characteristics within the fuel rod bundle using CFD methodology”, Nuclear Engineering and Design, vol.240, pp: 3078-3086, 2010.
27.Cheng S, Chen H, Zhang X, “CFD analysis of flow field in a 5× 5 rod bundle with multi-grid”, Annals of Nuclear Energy, vol.99, pp: 464-470, 2017.
28.毛曉輝，「帶定位格架的棒束通道內三維流場研究」，哈爾濱工程大學，碩士論文，2007.
29.Holloway M V, Beasley D E, Conner M E, “Single-phase convective heat transfer in rod bundles”, Nuclear Engineering and Design, vol.238, pp: 848-858, 2008.