Investigation of Bolgiano-Obukhov Scaling in Mixed Convective Flow with a LES Model of the Gallium Thermal-Hydraulic Experiment Facility

In sodium-cooled fast reactors, transient thermal stratification of the sodium coolant within the reactor components can cause severe thermal stresses. This thermal stress phenomena after related occurrences and/or during severe accident conditions can lead to vessel/component structure failure. Therefore, a thorough understanding of thermal stratification phenomena is critical to operational reliability and licensing efforts.Turbulent scaling theories can be used to describe the underlying mechanics contributing to stratification. In particular, Bolgiano-Obukhov (BO59) scaling is of interest in liquid-metal flows for its inclusion of buoyancy in the flow. However, the instantaneous velocity and temperature time series data required for investigating the presence of BO59 scaling is lacking. In an effort to augment the data sets available, the use of high-fidelity computational fluid dynamics (CFD) simulations to generate data capable of observing BO59 scaling is of interest.This study focuses on efforts in modeling the Gallium Thermal-hydraulic Experiment (GaTE) facility using large eddy simulations in Nek5000. The GaTE facility was designed as a scaled-down model of the Advanced Burner Test Reactor plenum to investigate thermal stratification within liquid-metal flows under a variety of operational conditions. Instantaneous temperature and velocity data are generated by the CFD model of GaTE during a forced flow transient exhibiting mixed convection with Ri = 0.722.In general, the data have shown evidence of BO59 scaling throughout the plenum, especially with the momentum spectra and cospectra, indicating that the simulation is likely capable of generating the necessary instantaneous velocity and temperature data required for observing the BO59 microscale in liquid-metal flows. It has been determined that future investigation is needed to understand the lack of agreement in the spectra for the lower plenum height region and to assess the presence of BO59 scaling in mixed convection regimes with greater influence of natural convection effects.