Simulations of PANDA and SPARC experiments on containment atmosphere mixing caused by vertical gas injection

Highlights: • A fluid-dynamics model within an open-source CFD code was improved to simulate experiments on containment atmosphere mixing. • The model was validated against 10 experiments performed in PANDA and SPARC facilities. • Various possibilities to reduce the computational domain for practical reasons were considered. • Effects of reduced numerical domain is assessed and the suitability of the reductions is discussed. Several experiments of interaction of air or steam jet with a horizontal helium rich layer in a closed vessel representing a NPP containment, which were performed in PANDA and SPARC experimental facilities, are simulated on the local instantaneous scale using the Unsteady Reynolds Averaged Navier Stokes approach. Axisymmetric two-dimensional and three-dimensional numerical models of cylindrical vessels are developed, and the effects of numerical domain reduction are studied. The mixing process is simulated as a single-phase flow with common momentum and energy equations. Consequently, an additional term accounting for enthalpy diffusion due to compositional changes is implemented into the energy equation. Included gas species mass fractions are considered as passive scalars and are calculated using the transport equation. However, the term describing the molecular diffusion cannot be neglected and had to be added to the diffusion equation implemented in the default OpenFOAM computational fluid dynamics code that was used. The k-ε turbulence model with additional turbulence generation and dissipation due to buoyancy is used for turbulence modelling. The comparison of simulation and experimental results shows that the improved physical model is able to successfully describe the phenomena in several experiments performed in different facilities with different initial and boundary conditions.