Numerical simulation and validation of submerged isothermal liquid metal jets

Abstract

Abstract

A key phenomenon under examination in liquid metal (LM) cooled nuclear reactors is the formation and evolution of submerged, axisymmetric, round LM jets in the upper plenum region, with particular emphasis on the influence of geometric configuration and density stratification on the development and stability of these flow structures. Experimentally, characterization of the optically opaque LM flow fields is performed using ultrasonic Doppler velocimetry (UDV). The primary objective of this study is to employ existing experimental data to validate computational models that can subsequently be used as predictive tools for simulating other LM coolant applications. Using computational fluid dynamics (CFD) software, the evolution of neutrally buoyant jets is analyzed and compared against theoretical descriptions. Unobstructed and obstructed inlet configurations are investigated over a range of injection flow rates and assessed relative to classical free-shear round jet theory. A modified k– ɛ turbulence model, with coefficients specifically calibrated for axisymmetric jet flows, is applied to characterize the behavior of confined pipe jets and obstructed LM jets over a range of inlet conditions, yielding results consistent with established empirical pipe jet correlations. For the Gallium Thermal–hydraulic Experiment (GaTE), good agreement between CFD predictions and theoretical expectations was obtained when reduced effective inlet diameters were adopted, as opposed to the assumptions of isothermal, unconfined round jet theory in an infinite domain. CFD models for obstructed jet flow were further validated experimentally in the presence of the upper internal structure (UIS) of the GaTE facility, with agreement demonstrated against the available experimental velocity measurements. The mean relative deviation between the experimental and computational results is determined to be less than 15%.