Numerical simulations of counter-current two-phase flow experiments in a PWR hot leg model

In order to improve the understanding of counter-current two-phase flows and to validate new physical
models, CFD simulations of 1/3rd scale model of the hot leg of a German Konvoi PWR with rectangular
cross section was performed. Selected counter-current flow limitation (CCFL) experiments at the Helmholtz–
Zentrum Dresden–Rossendorf (HZDR) were calculated with ANSYS CFX 12.1 using the multi-fluid
Euler–Euler modeling approach. The transient calculations were carried out using a gas/liquid inhomogeneous
multiphase flow model coupled with a k-x turbulence model for each phase. In the simulation, the
surface drag was approached by a new correlation inside the Algebraic Interfacial Area Density (AIAD)
model. The AIAD model allows the detection of the morphological form of the two phase flow and the
corresponding switching via a blending function of each correlation from one object pair to another.
As a result this model can distinguish between bubbles, droplets and the free surface using the local
liquid phase volume fraction value. A comparison with the high-speed video observations shows a good
qualitative agreement. The results indicated that quantitative agreement of the CCFL characteristics
between calculation and experimental data was obtained. The goal is to provide an easy usable AIAD
framework for all Code users, with the possibility of the implementation of their own correlations.