MODELLING THE THERMO-SOLUTAL CONVECTION, SHRINKAGE FLOW AND GRAIN MOVEMENT DURING GLOBULAR EQUIAXED SOLIDIFICATION IN A MULTI-PHASE SYSTEM I.THREE-PHASE MODEL
等轴球晶凝固多相体系内热溶质对流、补缩流及晶粒运动的数值模拟Ⅰ.三相流模型

A three-phase flow model has been developed to simulate the solidification process of globular equiaxed grains based on the volume averaging and Eulerian-Eulerian methods. The three phases, liquid, solid and air, share a single pressure field. The basic conservation equations of mass, momentum and enthalpy, and a user defined conservation equation of grain density have been solved for each phase. The thermal and mechanical (drag force) interactions among the phases have been considered. Grain nucleation, growth rate (mass exchange), solute partitioning at the liquid/solid interface and solute transport have also been accounted for. Due to the low density, the air phase floats always at the top region, forming a definable air/liquid melt interface, i.e. free surface. By tracking this free surface, the shrinkage cavity in an open casting system can be modeled. As the temperature and concentration dependent density and solidification shrinkage are explicitly included, the thermo-solutal convection, together with feeding flow and grain movement can be taken into account.