Numerical Simulation of Two-Dimensional Film Flow using CUPID1.8 Code

Since CUPID (Component Unstructured Program for Interfacial Dynamics) code has been developed, various verification and validation (V-V) problems were solved to confirm not only the numerical stability, robustness and accuracy, but also the adequacy of physical models in CUPID code. Recently, V-V has being performed for an interfacial drag model as well as a wall friction model. The interfacial friction plays important roles in two-phase flow problems such as a free surface in a large pool, horizontally stratified flow in cold legs, film flow in a downcomer, and so on. In particular, the interaction between the falling liquid film and the steam flow induce the two-phase multi-dimensional film flow when the emergency core coolant is injected into the upper downcomer during the reflood phase in the large break loss of coolant accident (LBLOCA). In this case, the interfacial drag force determines the reflood coolant into the core. Two-dimensional film flow experiments performed in Korea Atomic Energy Research Institute (KAERI) was used to verify the interfacial drag model in CUPID1.8 code. In addition, the sensitivity of interfacial drag models on the film flow was also numerically investigated. Two-dimensional film flow experiment was simulated to assess the interfacial drag model in CUPID1.8 code. The simulation results showed that CUPID1.8 reasonably predicted the liquid film flow and its behavior due to the drag force by air flow. However, the quantities of local velocity vectors showed some discrepancies due to the large interfacial drag force in CUPID1.8 code. This result indicates that further improvement and validation of the interfacial drag model are required. In addition, the turbulence models for each phase should be validated simultaneously since very complicated two-phase mixing phenomena occur when the injected water encounters laterally blowing air and forms steady liquid film. The turbulence model may affect velocity distributions of the liquid film and also the air