LES AND RANS MODELING OF AN 84-PIN HEXAGONAL ROD BUNDLE WITH SPACER GRID

As part of an ongoing Integrated Research Project (IRP), detailed investigations of the flow and heat transfer characteristics of an 84-pin hexagonal rod bundle representing a potential modular gas-cooled fast reactor design have been performed. The rod bundle features P/D of 1.5 and a large central guide tube, along with simple spacer grids and an outer enclosure. The primary focus of the current work is modeling and simulation of this geometry using a range of computational techniques. These include high-fidelity Large Eddy Simulation (LES) and Reynolds-Averaged Navier-Stokes (RANS) approaches. The flow predictions are validated at Reynolds number of roughly 12000 using matched index of refraction Particle Image Velocimetry (PIV) experimental data that were also generated as part of the IRP. Many characteristics of the experimental flow are replicated in the LES and RANS runs, and a general agreement between simulation and experiment is shown. The LES shows notably better agreement with the turbulent kinetic energy downstream of the grid as compared to RANS. The experimental and high-fidelity data will be used to inform the closures for a novel multiscale methodology. The high-level goal of the work is to use the high-fidelity data to yield improved multiscale thermal analysis techniques for solving fuel performance problems of direct relevance to industry.