Numerical and Experimental Analysis on a Planar Jet with Heated Co-Flow at Medium- and Low-Prandtl Number Values

The Multi-purpose hYbrid Research Reactor for High-tech Applications (MYRRHA) is a pool-type fast reactor cooled by the LBE liquid metal under design at SCK•CEN. Thermal hydraulics is a key aspect in the design phase and safety analyses of such advanced systems. In large compartments as the upper and lower plena, typical flow patterns are characterized by multi-jet interactions. Hence, the jet flow can be considered as one of the most representative flow regimes to be analysed. General purpose Computational Fluid Dynamics (CFD) tools assume turbulent heat fluxes to be analogously modelled to Reynolds stresses in the time-averaged momentum and energy equations respectively. This hypothesis (Reynolds analogy) is mainly valid for forced convection flows with molecular Prandtl number (Pr) of the order of unity. On the other hand, liquid metals are characterized by significantly lower Pr values, the Reynolds analogy is not applicable and innovative Turbulent Heat Transfer (THT) models have been proposed. The latter have mainly been developed on wall-confined flows since there is still a limited database of reference to wall-unconfined flows. With the aim to provide more insights in jet flows at low-Pr values, the MYRTE wind tunnel was designed and operated at VKI to experimentally investigate a forced planar jet with heated co-flow with air (Pr = 0.71) and He-Xe gasses mixture (Pr = 0.2). The experimental database was compared with Reynolds Averaged Navier-Stokes (RANS) simulations to test Reynolds analogy-based and four-parameter THT models. Considering the actual configuration of the MYRRHA reactor and its primary coolant (Pr = 0.025), this study represents an intermediate milestone in the THT modelling for industrial CFD analyses of nuclear liquid metal-cooled systems.