CFD simulations of stratified layer erosion in MiniPanda facility using the tailored CFD solver containmentFOAM

Abstract

Turbulent gas mixing in a buoyant flow with density gradient is an important physical mechanism in many applications ranging from industrial gaseous emissions into the atmosphere to nuclear reactor containment flows. With relevance to nuclear reactor safety, erosion of a stratified light gas layer by a momentum-driven or buoyancy-driven jet is often studied owing to the possibility of flammable hydrogen rich layer formation and associated combustion risks in the containment as it occurred at the Fukushima Daiichi accident. In the recent developments of CFD models for containment flows, it is identified that buoyancy contribution in the turbulence production and dissipation terms irrespective of the turbulence model plays a significant role.Owing to its open-source code and rapid developments in OpenFOAM, a tailored solver containmentFOAM based on OpenFOAM libraries is currently being developed at Forschungszentrum Jülich with significant improvements and modeling choices. In the present paper, the MiniPanda experiments performed at ETH Zürich, Switzerland, are chosen for performing the URANS simulations with containmentFOAM to evaluate its capabilities while giving specific attention to the transient evolution of the flow field. In addition to the classical validation of helium concentration profiles, the temperature measurements extracted from TWMS (Temperature Wire Mesh Sensors) and the jet penetration analyses are utilized to enhance the understanding of turbulent heat and mass transfer. The impact of turbulence production and dissipation terms due to buoyancy on the turbulent gas mixing and thermal transport is demonstrated in detail. Their consideration reveals a visible impact on the mixing process, while the model formulation SGDH or GGDH has a minor impact in this flow configuration. Furthermore, the impact of the mixture model for the fluid transport properties is investigated. It is clearly demonstrated that the Wilke mixture law provides more consistent results in the case of He-air mixing.