Development and Validation of High-precision Cfd Method with Volume-tracking Algorithm for Gas-liquid Two-phase Flow Simulation on Unstructured Mesh

In design studies of Japanese sodium-cooled fast reactors, a compact size reactor vessel is expected to be employed for economical advantages. However, such a design makes coolant velocity higher and may result in occurrence of gas entrainment (GE) phenomena. Since the GE is highly non-linear and too difficult to predict its onset condition by theoretical methods, we are developing a high-precision CFD method to evaluate the GE accurately. The CFD method is formulated on unstructured meshes to establish accurate geometric modeling of complicated reactor systems. As for two-phase flow simulations, a high-precision volume-of-fluid algorithm was employed and newly formulated on unstructured meshes. In the formulation process, a volume-conservative algorithm and a new formulation establishing the mechanical balance between pressure and surface tension were introduced. The developed CFD method was verified by solving well-known driven-cavity and Zalesak’s slotteddisk rotation problems to show the simulation accuracy. Then, we simulated a rising bubble in liquid under Bhaga et al’s experimental conditions. As a result, the developed method showed good agreement with the experiment. Finally, the developed method was validated by simulating the GE phenomena in the basic experiment. The developed method succeeded in reproducing the occurrence of the GE under the experimental GE condition.