Investigation of Turbulence Characteristics of the Flow in a 1x3 Fuel Rod Bundle with Spacer Grids Using Computational Fluid Dynamics Method

In this paper the effects of simple support grids, without mixing vanes, on flow through a 1 x 3 rod bundle has been investigated with CFD methodology, and the most appropriate turbulence model reflecting the physics of the flow has been determined. Experimental studies performed in the flow laboratories of Penn State University have been referenced in comparison with the simulation results, (Wheeler, 2014) where single-phase flow in the subject rod bundle was examined. In the first part of the study, choice of computational grid study has been carried out on tetra, hybrid and poly type meshes in order to determine the most appropriate type and density. In this section, only k - epsilon standard and RSM LPS turbulence models have been utilized. In the second part, using the mesh determined in the first section, comparison has been made covering all turbulence models examined in the study. Velocity and turbulence intensity distribution in the center of the rod pitch, upstream and downstream of the spacer grid at -3d(h), +3d(h) and +40d(h) locations have been examined and compared with the experimental data. The results of the study reveal the effects of the mesh type on calculations, where the hybrid mesh, having the greatest number of structured elements, exhibits better performance than the others. Comparison between numerical and experimental results of rod central velocities shows an overall agreement with all turbulence models, while complex models (except k - epsilon RNG) present better results than the two-equation models. As a result of this study, flow through a simple support grid has been examined and the most appropriate turbulence model reflecting the physics of the flow has been determined.