Validation of a Morphology Adaptive Multi-Field Two-Fluid Model Considering Counter-Current Stratified Flow with Interfacial Turbulence Damping

Stratified flows are one of the most important multiphase flow regimes for safety analyses of the loss-of-coolant accident in pressurized water reactors. The present paper considers simulations of an isothermal counter-current stratified flow case in the channel of the WENKA (Water Entrainment Channel Karlsruhe) experiment using a morphology adaptive multi-field two-fluid modelling framework. A consistent momentum interpolation approach is applied together with the partial elimination algorithm, as it is required for strong momentum coupling, which enforces the no-slip condition at the interface and mirrors the behaviour of a homogeneous model. To model the turbulent flow conditions near an interface, the framework is extended with a turbulence damping model based on the damping scale formulation from the literature, which is introduced into the k-omega SST (Shear Stress Transport) turbulence model. The presented modelling approach is validated with experimental data for the pressure difference and vertical profiles of volume fraction, velocity and turbulent kinetic energy. Results of a mesh sensitivity study of the model are presented. Simulations were performed on two- and threedimensional models of the channel geometry. Two turbulence damping strategies are investigated: symmetric, with damping in both phases, and asymmetric with damping only in the gas phase. The comparison shows that the asymmetric approach offers improved prediction of turbulent kinetic energy on the liquid side of the interface, but with a cost of diminished accuracy of the predicted velocity profiles on the gas side.