基于虚拟体积力动量源的燃料组件热工水力数值求解方法

Method of Simulating Thermal-hydraulic Behavior of Fuel Assembly Based on Virtual Body Force Momentum Source

针对计算流体力学(CFD)与三维精细化建模方法应用于反应堆燃料组件热工水力分析时普遍面临计算量较大和计算效率较低的问题,本文基于搅混翼对流场及温度场的阻流、导流、搅混与换热强化等方面的影响机理,通过建立搅混翼的虚拟体积力数理模型来考虑搅混翼对热工水力的影响。以两通道模型为研究对象,将虚拟体积力模型以动量源项的形式加入无翼片通道中,获得了带搅混翼通道的热工水力特性。该方法避免了直接对燃料组件中的复杂搅混翼结构进行贴体网格建模,可显著简化建模过程、降低计算量及提高计算效率。通过与实验数据及传统贴体网格建模结果的综合对比分析,验证了模型的有效性。研究结果表明:搅混翼对棒束通道流场及温度场的综合影响,可等效为结构对流体施加的某种作用力改变了流体质点运动规律,从而表现出特殊的热工水力现象;虚拟体积力动量源模型所计算的流速、压降及换热系数等关键热工水力参数,与实验数据及传统贴体网格计算结果吻合良好,并能适应不同流速工况。

Aiming at the problems of too large calculation amount and poor computational efficiency when applying the methods of computational fluid dynamics(CFD)and three-dimensional refined modeling to the analysis of thermal-hydraulic behaviors of the fuel assemblies with mixing vane grids in pressurized water reactor(PWR),a virtual body force mathematical model was established based on the influence mechanism of the mixing vans on the flow and temperature fields in terms of flow resistance,flow diversion,fluid mixing and heat transfer enhancement to investigate the effect of the mixing vanes.The virtual body force model was added to a two-subchannel rod bundle model without mixing vane in the form of momentum source term,and the flow and temperature fields downstream of a mixed vane spacer grid were captured.This method significantly simplifies the modeling process,reduces the amount of calculation and improves the calculation efficiency.The effectiveness of the virtual body force model was verified through a comprehensive comparative analysis with experimental data and the calculation results of traditional body-fitted mesh modeling.The study shows that the comprehensive effects of the mixing vane spacer grid on the flow and temperature fields can be assumed to be that the mixing vanes exert a certain force on the fluid.The force changes the law of fluid particle motion,which is the reason causing special thermal-hydraulic behaviors.The key thermal-hydraulic parameters such as flow velocity,pressure drop and heat transfer coefficient calculated by the virtual body force model established are in good agreement with experimental data and calculation results of the body-fitted mesh modeling.