NUMERICAL STUDY ON THE EFFECTS OF VANE ANGLE AND DIMPLE ON THE THERMAL HYDRAULIC PERFORMANCE OF A PWR FUEL ASSEMBLY

摘要

As the most important structure to enhance fuel assembly CHF and increase economic efficiency of reactors, mixing vane spacer grids have always been the focus of numerical simulations and experimental studies. Currently, the design of commercial mixing vane grids strongly depends on full-scale thermal hydraulic experiments, which are expensive and time consuming. With the recent development of computer technology, numerical studies using computational fluid dynamics (CFD) have been conducted to enhance the understanding and design of commercial mixing vane grids. In current numerical simulations of spacer grid mixing effect, most researchers do not distinguish the impact from different components, but look to encompass all component effects of the entire spacer grid including those of vanes, dimples, springs, and straps for their overall mixing performance. In this paper, two spacer grids were modeled to obtain the effects of the mixing vane and dimple respectively. Four grids of different vane angles and three grids of different dimple shapes were examined. First, the effect of vane angle was examined using four different grids of different vane angles without the presence of dimples or spring. Then, both mixing vanes and dimples were added to the grids in order to investigate the compound mixing effects caused by dimples with the presence of mixing vane. During this series of study, the dimple shape was changed while keeping the vane angle fixed. Two different commercial codes, CFX and STAR-CD, were applied to study the flow field under the same operating conditions to provide code-to-code benchmarking. As a basic verification, the results of CFD simulated pressure drop were compared against experimental data. Relatively good agreement between the experimental and simulated pressure drops was obtained. Code to code comparison indicated that different CFD codes provide similar results with slight variations. Further work is needed with more experimental data to verify the turbulence effects and benchmark the CFD results under various thermal hydraulic conditions.