Multiphasing CFD

Computational fluid dynamics for multiphase flows is an emerging field. Due to the complexity and divergence of multiphase thermal and hydraulic problems, further development of multiphase flow modelling, closure laws and numerical methods is needed in order to achieve the general purpose and optimised CFD (Computational Fluid Dynamics) methods, which will be applicable to the wide variety of multiphase flow problems. In the paper, an original approach to the various aspects of multiphase CFD modelling is presented. It is based on the multi-fluid modelling approach, development of necessary closure laws and derivation of appropriate numerical methods for efficient governing equations solution. Velocity and pressure fields are solved with the SIMPLE (Semi-Implicit Method for Pressure-Linked Equations) type pressure-corrector method developed for the multiphase flow conditions. For the solution of scalar parameters transport equations both implicit and explicit methods are presented. The implicit method is suitable for steady state, slow transients and problems without the sharp fronts propagation. Explicit method is developed in order to predict scalar parameters fronts propagation, as well as phase interface tracking problems. The challenge towards the multiphase flow solution on both the macro and micro level is presented in order to perform multiphase CFD simulations and analyses of multiphase flows in complex geometry of nuclear power plant components, such as nuclear fuel rod bundles thermal-hydraulics. Presented methodology and obtained CFD results comprise micro-scale phenomena of phases’ separation, interface tracking, heated surfaces dry-out and critical heat flux occurrence, as well as macro-scale transport and distributions of phase volumes.