Session: 08-03: Computational Fluid Dynamics (CFD) and Applications - III

Paper Number: 135617

135617 - Understanding the Flow Anisotropic Turbulent Flow in the Subchannel of Fuel Assembly Under Effect of the Bare Rod and Mixing Vane Grid by Les 

Abstract: 

The Mixing Vane Grid(MVG) is an integral component of fuel assemblies in nuclear reactor core, playing the role of supporting the rod bundle and mixing the coolant. The flow of coolant through the mixing vanes within the MVG, which intensifies the turbulence, exerts a significant influence on the reactor core's Critical Heat Flux(CHF). This enhancement of turbulence directly correlates with improved heat transfer performance at the wall, thus bring both the safety and economic efficiency of the reactor. The geometric asymmetry of subchannels in the fuel assemblies of Pressurized Water Reactors(PWRs) introduces an element of flow anisotropy. This anisotropy is a critical factor in the accurate prediction of the onset of two-phase boiling and CHF in the rod bundle subchannel systems.

 

Traditional Reynolds-Averaged Navier-Stokes(RANS) turbulence models have limitations in predicting the anisotropic turbulent flow within rod bundle subchannels. This paper addresses this challenge by employing Large Eddy Simulations(LES) to investigate the anisotropic flow characteristics. Firstly, the numerical method was validated by comparing with Emilio’s previous work under different P/D. The DNS and experimental data of P/D were used to validate the LES model settings. Then the anisotropic turbulent flow was investigated in 2x1 and 3x3 rod bundle subchannels. This study includes a comparative analysis of the impact of different rod bundle geometries on the flow anisotropy. Furthermore, it delves into the influence of the MVG on the anisotropic turbulent flow within rod bundle subchannels, particularly under a 3x3 MVG structure. The study meticulously examines the effects of variations in vane angles within the mixing vanes on flow anisotropy, revealing that changes in these angles can induce varying degrees of turbulence and pressure drop in the flow field. The research systematically analyzes the evolution of turbulent anisotropy within subchannels under the combined effects of the bare rod bundle channels and the MVG. This involves a detailed examination of the flow field characteristics, contributing significantly to the understanding of complex flow phenomena in fuel bundles. The insights gained from this study lay the groundwork for the development of an upgraded Unsteady RANS(URANS) model capability of accurately reflecting the effects of anisotropy. This advancement is pivotal in enhancing the predictive accuracy and reliability of models used in the nuclear industry.

 

Moreover, the findings from this research are instrumental in informing the design of high-performance fuel assembly spacer grids. By understanding the intricate dynamics of flow anisotropy and its impact on heat transfer and fluid dynamics within nuclear reactor cores making the development of more efficient and safer nuclear fuel assemblies.

 

Keywords: Subchannel, Fuel assembly, Anisotropic turbulent flow, Mixing vane grid, LES

Presenting Author: Siwei Qi Southeast University

Presenting Author Biography: Siwei Qi is a graduate student at Southeast University, China. He is studying numerical simulations of flow and heat transfer between fuel rod bundles. His research interests include computational fluid dynamics, heat transfer, and nuclear fuels.

Authors:

Siwei Qi Southeast University
Bin Han Southeast University
Tianyang Xing Southeast University
Xiaoliang Zhu Southeast University
Bao-Wen Yang DEQD Institute for Advanced Research in Multiphase Flow and Energy Transfer
Yuanyuan Yin Southeast University
Aiguo Liu DEQD Institute for Advanced Research in Multiphase Flow and Energy Transfer
Shenghui Liu Southeast University