DIRECT NUMERICAL SIMULATION OF MIXING PHENOMENA IN THE UPPER PLENUM OF ADVANCED REACTORS

The conceptualization and development of advanced nuclear reactors encompasses challenging fluid-flow concerns that significantly impact their operational safety and efficacy. The establishment of a comprehensive numerical database focused on high-fidelity data holds promising potential in facilitating the formulation of accurate and cost-effective reduced-resolution heat transfer models. These models can be designed based on a multiscale hierarchy developed as part of the recent U.S. Department of Energy-funded Center of Excellence for Thermal Fluids Applications in Nuclear Energy, which represents a significant stride toward resolving industry-specific challenges associated with the heat transfer behavior of advanced reactors. In this paper, we consider Direct Numerical Simulation of the upper plenum with discharging jets of high-temperature gas-cooled reactors. Two isothermal cases at Re = 10622 and 4097 have been considered following the experimental setups of TAMU and MiGaDome facilities. The low Prandtl number fluid (Helium) is considered for all simulations. First and second-order statistics are investigated, and improvements of the agreement with experimental data have been observed compared to previous LES studies. Moreover, the Proper Orthogonal Decomposition (POD) is applied to reveal and illuminate the flow behaviors in the upper plenum. The generated high-fidelity DNS data will be utilized alongside datadriven methods to improve turbulence modeling closures.