Numerical Simulation On The Characteristics Of Complex Flow And Heat Transfer Of Rod Bundle With Spacer Grid

The turbulent flow behavior and heat transfer performance of rod bundle with spacer grid have significant effect on the thermal-hydraulic characteristics and the reactor's safety in pressurized water reactor. Because of the high cost and long research period of the experimental study, the numerical simulation on thermal-hydraulic characteristics of rod bundle with spacer grid has been paid wide attention. In this paper, the numerical calculation of the characteristics of complex flow and heat transfer of 5?5 rod bundle with spacer grid has been carried out based on structure of opening fuel assembly in pressurized water reactor. The effects of different turbulence models on the numerical results of turbulent flows in complex structures are analyzed, and identified a more suitable model for the present study of complex structure and the thermal boundary conditions. In order to fully consider the influence of the complex structure on the flow behavior and heat transfer in the fuel assembly, a construction method of mesh which suitable for complex structure is proposed. For mesh quality of numerical computation of the spacer grid includes dimple, mixing vane and spring and is well. The results of CFD calculation are in accordance with the experiment in this study. Meanwhile, this article thoroughly study the impact of spacer grid especial for mixing vane on flow and heat transfer, and observing the normalized Nusselt number is gradually decay along the flow direction. The normalized Nu number, less than 1.0 just near the z/Dh=18.0, indicates the weakness of heat transfer capability, which is reasonably revealed in lateral velocity pulsation. Several different types of vortex which includes vortex identification, vortex generation and vortex evolution induced by mixing vane are analyzed, and the change laws of vortex evolution are the same as the swirl factor, which the swirl factor gradually increasing before z/Dh=4.0 then decay along the flow direction. Two types of spacer grids are investigated, including spacer grid A and spacer grid B. According to the numerical study, the swirl ability of spacer grid A greater than B and the void fraction of external rods higher than internal rods in spacer grid A. To study the characteristics of swirl in rod bundle, the evolution characteristics in the sub channels are compared and the obvious difference between subchannels are discovered. In addition,different research methods also have great differences in the study of the rod bundle channel of vapor liquid two phase flow, the sub channel can be chosen as the reference object when the emphasis is given to the research of the secondary flow and the fuel rod can be chosen as the reference when the emphasis is given to the research of the void fraction.