In High Temperature Gas-cooled Reactors (HTGR), gas flow patterns are very complex and reduced order models (1D or 2D) may be too simplified to predict accurate reactor performance. 3D Computational Fluid Dynamics (CFD) models can help provide the detailed information needed to optimize the reactor thermal performance. The main objective of this work is to validate the CFD models with data of a 1/16th scaled Very High Temperature Reactor (VHTR) upper plenum measured at Texas A&M University.
In this paper, the flow characteristics of a single isothermal jet discharging into the upper plenum was investigated using Nek5000 Large-Eddy Simulation (LES) CFD tool. Several numerical simulations were performed for various jet Reynolds numbers ranging from 3,413 to 12,819. Grid independent study was performed. The numerical results of mean velocity, root-mean-square fluctuating velocity, and Reynolds stress were validated with the benchmark data. Good agreement was obtained between simulated and measured data for axial mean velocities, except near the upper plenum hemisphere. The maximum predicted errors for axial mean velocities at various normalized coolant channel diameter heights of 1, 5 and 10 are 1.56%, 1.88% and 3.82%, respectively. Also, the predicted root-mean-square fluctuating velocity and Reynolds stress are qualitatively agreed with the experimental data.