Experimental turbulence analysis of fuel bundle with spacer grids

Rod bundles are widely used in industry today with applications ranging from nuclear reactors, heat exchangers, and steam generators. Accurately modeling the inherently unsteady and turbulent flow within these rods is essential in order to design for optimal efficiency while controlling vibration, noise and heat transfer. The problem complicates further when spacer-grids are used within the rods to maintain separation and structural rigidity. Computational modeling can be a useful alternative to the costly process of manufacturing and testing prototypes, but its accuracy needs to be checked with detailed experimental data. This paper describes an experimental database obtained using two-dimensional Time Resolved Particle Image Velocimetry (TR-PIV) measurements within a 5 x 5 rod bundle with spacer-grids. One of the unique characteristic of this set-up is the use of the Matched Index of Refraction technique employed in this investigation which consists of immersing plastic rods with a similar index of refraction as the one for water to achieve optical transparency across the spacer grid. This unique feature allows flow visualization and measurement within the bundle without rod obstruction. This approach also allows the use of high temporal and spatial non-intrusive dynamic measurement techniques namely TR-PIV to investigate the flow evolution below and immediately above the spacer. The data base presented includes explanation of the various cases tested such as boundary conditions, rig dimensions, measurement zones, and the test equipment in order to provide a good base for Computational Fluid Dynamics (CFD) simulations. Turbulence analysis of the obtained data is provided in order to gain insight of the physical phenomena and to compare the possible results obtained from computational simulations.