Numerical Study On Two Phase Flow With OPENFOAM

The two phase flow, related to the flow regime and heat transfer in the assemblies of the nuclear reactor, is an important factor adopted to assess the performance of thermal hydraulic of reactor and safety margin. Therefore, numerical simulation of two phase flow has achieved significant interests of research institutions. In the past few years, extensive R&D activities have proposed different interfacial models to describe the momentum exchange between phases. However, they can only be applied to very limit situations. It is of great important to develop a new model with a wide application area.The main objectives of this thesis are: (i) to build and validate a new open source CFD platform, (ii) to develop a new solver which adopts two fluid model based on this new platform, (iii) to improve the drag model for two phase flow and validate it based on this new solver, and (iv) to validate the existing lift model.The thesis consists of several steps:The first step is devoted to the build-up and validation of the new CFD platform. (i) The new open-source CFD platform has been built up. (ii) The new platform is validated firstly by simulation the interfacial shape in windowless spallation target in ADS (accelerator driven system). (ii) By simulating the flows in subchannel of tight lattice configuration with large eddy simulation, it also verifies that the OpenFOAM has great effectiveness in single phase simulation.In the second step, based on the new CFD platform, the two fluid model in which semi-conservative form of momentum equations are utilized to develop a new solver for bubbly flow.In the third step, the drag model of two phase flow is studied. Based on the wake effect, the drag model is improved. The bubbly flow in a large diameter vertical pipe is studied by numerical simulation in which new solver is utilized. It's indicated that the new model obtains better results on drag force and relative velocity of two phases. The results also show that a turbulence model for two phase flow plays an important role in the simulation of the velocity distribution.In the forth step, by the numerical calculation with lift model, the results shows that the existing models and the wall lubrication force models cannot predict the void fraction peaks near the wall correctly. Meanwhile since the velocity distribution near the wall cannot be obtained, this deficiency also affects the results of void fraction near the wall.The numerical study in this thesis focus on the build-up of a new open-source CFD platform, and this platform is applied to the simulation of two phase flow. This work will be useful for the future development of CFD program.