Volume average of two-fluid RANS equations and a priori estimation of subgrid terms on subcooled boiling experiments.

A statistic-volume averaged two-fluid model, convenient for subchannel and system codes in nuclear industry, is established from RANS equations of Neptune_CFD code and leads to the appearance of subgrid terms. A database of simulations is made on experiments with flow representative of nuclear reactor cores with cylindrical (KIT) and subchannel (PSBT) configurations. The subgrid terms are then compared to the convection terms on the database of 82 test cases. Concerning momentum and energy equations, subgrid terms reach respectively 7.5% and 16% of convection terms. Overall, the comparison shows that dispersion terms are always greater than turbulence terms, but both remain in the same order of magnitude, and are not negligible compared to convection. Moreover, the geometry has an impact on the dispersion terms. This observation suggests that caution should be exercised when using correlation established on a different geometry. • A macroscopic formulation is established from the RANS equations of Neptune_CFD. • A validated CFD database of subcooled boiling flows is created. • An a priori evaluation of subgrid terms is done based on CFD numerical simulations. • The subgrid terms are not negligible compared to the convection ones. • The channel geometry has an impact on dispersion terms values. [ABSTRACT FROM AUTHOR]