Exploration of the double-diffusive convection during dendritic solidification with a combined volume-averaging and cellular-automaton model

A two-dimensional model is built and used to study thermo-solutal (double diffusive) convection generated during the solidification of a binary mixture in a rectangular enclosure cooled from bottom and side walls. In order to catch the smallest solute plumes scale the solidification model simulates directly the envelope of the columnar dendrites with a cellular automaton model. The mushy interior of the dendrite is modelled with a volume averaging method. The model predicts the occurrence of several flow regimes during solidification, such as turbulent, stratified and meandering flows. As a result or origin of the two dimensional meandering flow pattern, the concentration field is found to be organised in horizontal layers of uniform concentration. Those layers are separated by very thin boundary layers so that the concentration varies vertically in staircases.