Simulation of multi-dimensional heterogeneous and intermittent two-phase flow by using an extended two-fluid model

A new gas-liquid two-phase flow simulation method has been developed based on the extended two-fluid model, which has capabilities of both the two-fluid and the interface-tracking models. The VOF (Volume of Fluid) technique has been introduced for suitable interface calculations. Interfaces of free surface and large bubbles are calculated directly by solving transport of a steep void fraction gradient corresponding to interface, while averaged behavior of microscopic dispersed bubbles and droplets are calculated in the two-fluid model scheme. It is expected that the present method can treat effects of significant kinetic interaction between the phases directly without empirical correlations. The calculated propagation of wet front in a dam break problem is close to experimental data. The predicted flow patterns of complex gas-liquid two-phase flow in a flat tube are quite similar to observations with a video camera. The present simulation will be a useful tool for predictions of integral behavior of thermal-hydraulic phenomena in large-scale nuclear power plants.