Numerical Simulation of Free Surface Flows With Heat and Mass Transfer

The paper presents CFD validation results for horizontal, stratified flows of sub-cooled water with condensation of saturated dry steam along the water surface. These are important flow phenomena relevant for pressurized thermal shocks (PTS). The experimental data for assessing the accuracy of the CFD results have been obtained in the LAOKOON test facility of Technische Universität München. Computational results have been obtained with the NEPTUNE_CFD and ANSYS CFX CFD codes. Co- and counter current flows with energy and mass transfer at the free surface have been simulated. The mathematical models used in the calculations are based on the Euler-Euler two-fluid model concept. The ANSYS CFX study investigated mainly the influence of two-phase flow model parameters, like interfacial length scales and interfacial heat transfer coefficients. The influence of using a homogeneous two-phase model versus a full two-fluid model was also examined. The NEPTUNE_CFD calculations were run with more advanced models for the interfacial drag coefficient and interfacial energy transfer. For instance, the interfacial energy transfer models were based on the surface renewal theory, and different approaches to calculate the interfacial area density were studied. Both CFD codes showed qualitative agreement with the data, but tend to under-predict the temperature in the water layer which is an important quantity to assess the effects of PTS. Unfortunately the LAOKOON data are not very detailed regarding inlet and outlet boundary condition, which makes a more thorough investigation of the discrepancies between predictions and data difficult.