Application of a new drag coefficient model at CFD-simulations on free surface flows relevant for the nuclear reactor safety analysis

This paper presents different CFD-simulations on flows which are relevant for nuclear reactor safety using a new modelling approach for the interfacial drag at free surfaces. The developed drag coefficient model was implemented together with the Algebraic Interfacial Area Density (AIAD) model (Höhne, 2009) into the three-dimensional (3-D) computational fluid dynamics (CFD) code ANSYS-CFX. The applications considered include the prediction of counter-current flow limitations (CCFL) in a PWR hot leg, the development of hydraulic jump during the air-water co-current flow in a horizontal channel, and pressurized thermal shock (PTS) phenomena in a PWR cold leg and downcomer. For the modelling of these tasks, an Euler–Euler approach was used. This approach allows the use of different models depending on the local morphology. In the frame of an Euler-Euler simulation, the local morphology of the phases has to be considered in the drag model.

To demonstrate the feasibility of the present approach, the computed main parameters of each case were compared with experimental data. It is shown that the CFD calculations agree well with the experimental data. This indicates that the AIAD model combined with new drag force modeling is a promising way to simulate the phenomena in frame of the Euler-Euler approach. Moreover the further validation of the model by including mass transfer effects should be carried out.